COLLEGE  OF  AGRICULTURE 
DAVIS,  CALIFORNIA 


4-0 


HISTOLOGY 


THE    ESSENTIALS 


OF 


HISTOLOGY, 


DESCRIPTIVE  AND  PKACTICAL. 


FOR    THE    USE    OF  STUDENTS. 


BY 


E.   A.   SCHAFER,    F.R.S., 

JODRELL  PROFESSOR  OF  PHYSIOLOGY  IN  UNIVERSITY  COLLEGE,  LONDON  ; 
EDITOR  OF  THE  HISTOLOGICAL  PORTION  OF  QUAIN'S  "  ANATOMY." 


THIRD    EDITION,   REVISED    AND    ENLARGED. 


'ILLUSTRATED  BY  MORE   THAN  300  FIGURES, 
MANY  OF   WHICH  ARE  NEW. 


PHILADELPHIA: 

LEA    BROTHERS    &    CO. 

1892. 

UNIVERSITY  OF  CALIFORNIA 

LIBRARY 

COLLEGE  OF  AGRICULTURE 
DAVIS 


PREFACE. 


THIS  BOOK  is  written  with  the  object  of  supplying  the  student  with 
directions  for  the  microscopical  examination  of  the  tissues.  At  the 
same  time  it  is  intended  to  serve  as  an  Elementary  Textbook  of 
Histology,  comprising  all  the  essential  facts  of  the  science,  but  omit- 
ting unimportant  details,  the  discussion  of  which  is  only  calculated  to 
confuse  the  learner.  For  a  similar  reason  references  to  authorities 
have  also  generally  been  omitted.  Most  of  the  illustrations  are  taken 
from  Quain's  Anatomy.  Of  the  remainder,  those  which  have  been 
selected  from  other  authors  are  duly  indicated ;  the  rest  have  either 
been  drawn  expressly  for  this  work,  or  have  been  transferred  to  it 
from  the  author's  Course  of  Practical  Histology, 

1  am  indebted  to  Dr.  Ferrier  for  permission  to  use  the  illustrations 
of  the  structure  of  the  spinal  cord  and  cerebral  cortex  which  have  been 
contributed  to  the  second  edition  of  his  book,  The  Functions  of  the 
Brain,  by  Mr.  Bevan-Lewis. 

For  conveniently  accompanying  the  work  of  a  class  of  medical 
students,  the  book  is  divided  into  forty-five  lessons.  Each  of  these 
may  be  supposed  to  occupy  a  class  from  one  to  three  hours,  according 
to  the  extent  to  which  the  preparations  are  made  beforehand  by  the 
teacher  or  are  prepared  during  the  lesson  by  the  students.  A  few  of 
the  preparations — e.g.  some  of  those  of  the  sense-organs — cannot  well 


vi  PREFACE. 

be  made  in  a  class,  but  it  has  been  thought  advisable  not  to  injure  the 
completeness  of  the  work  by  omitting  mention  of  them. 

Only  those  methods  are  recommended  upon  which  experience  has 
proved  that  full  dependence  can  be  placed,  but  the  directions  given 
are  for  the  most  part  capable  of  easy  verbal  modification  in  accordance 
with  the  ideas  or  experience  of  different  teachers. 


CONTENTS. 


INTRODUCTORY. 

PAGB 
ENUMERATION  OF  THE  TISSUES — GENERAL  STRUCTURE   OF  ANIMAL   CELLS,  1 


LESSON    I. 
USE   OF    THE  'MICROSCOPE — EXAMINATION    OF   COMMON    OBJECTS,          .  .  6 

LESSON  II. 

STUDY   OF   THE    HUMAN    BLOOD-CORPUSCLES, 10 

LESSON  III. 

ACTION    OF    REAGENTS    UPON    THE    HUMAN    BLOOD-CORPUSCLES,  .  .  .  15 

LESSON  IV. 

STUDY   OF   THE   BLOOD-CORPUSCLES    OF   AMPHIBIA, 18 

LESSON  V. 

THE   AMCEBOID    PHENOMENA    OF    THE   COLOURLESS    BLOOD-CORPUSCLES,         .  20 

LESSON  VI. 

EPITHELIUM — CELL-DIVISION, 24 


viii  CONTENTS. 

LESSON  VII. 

I'AOE 

COLUMNAR   AND    CILIATED    EPITHELIUM    AND    TRANSITIONAL    EPITHELIUM,  30 

LESSON  VIII. 

STUDY   OF  CILIA    IN    ACTION, 34 

LESSON  IX. 

THE   CONNECTIVE   TISSUES  :     AREOLAR   AND   ADIPOSE   TISSUE,      ...  37 

LESSON  X. 

THE   CONNECTIVE  TISSUES  (continued)  I   ELASTIC  TISSUE,   FIBROUS   TISSUE, 

DEVELOPMENT    OF   CONNECTIVE   TISSUE,       ......  45 

LESSON  XI. 

THE    CONNECTIVE    TISSUES   (continued)  :    ARTICULAR    CARTILAGE,          .  .  50 

LESSON  XII. 

THE    CONNECTIVE    TISSUES    (continued)  :     COSTAL    CARTILAGE,    FIBRO-CAR- 

TILAGE, 54 

LESSON  XIII. 

THE   CONNECTIVE   TISSUES   (continued)  I     BONE   AND    MARROW,   ...  57 

LESSON  XIV. 

THE    CONNECTIVE    TISSUES   (continued)  I     DEVELOPMENT    OF    BONE,      .  .  64 

LESSON  XV. 

STRUCTURE   OF   STRIATED   MUSCLE,     ...  .  .  .  .  .  .  72 

LESSON  XVI. 

STRUCTURE    OF    STRIATED    MUSCLE    (continued),  .....  75 


CONTENTS.  ix 

LESSON  XVII. 

PAGE 
CONNECTION     OF     MUSCLE     WITH     TENDON  —  BLOOD-VESSELS     OF     MUSCLE — 

CARDIAC    MUSCLE DEVELOPMENT    OF    MUSCLE — PLAIN    MUSCLE,  .  79 

LESSON  XVIII. 

STRUCTURE    OF    NERVE-FIBRES, 83 

LESSONS  XIX.  AND  XX. 

STRUCTURE  OF  GANGLIA — STRUCTURE  OF  NERVE-CELLS — STRUCTURE  OF 
NEUROGLIA-CELLS — DEVELOPMENT  OF  NERVE-FIBRES — WALLERIAN 
DEGENERATION,  ..........  90 

LESSON  XXI. 

MODES    OF   TERMINATION    OF    NERVE-FIBRES, 98 

LESSON  XXII. 

STRUCTURE    OF   THE   LARGER   BLOOD-VESSELS, 107 

LESSON  XXIII. 

SMALLER      BLOOD-VESSELS,      LYMPHATIC      VESSELS,      SEROUS      MEMBRANES, 

SYNOVIAL    MEMBRANES, .  .  .112 

LESSON  XXIV. 

LYMPHATIC    GLANDS,    TONSIL,    THYMUS, 121 

LESSON  XXV. 

THE   SKIN, 127 

LESSON  XXVI. 

STRUCTURE   OF   THE    HEART, 139 

LESSON  XXVII. 

THE    TRACHEA    AND    LUNGS, 143 


x  CONTENTS. 

LESSON  XXVIII. 

PAGE 
STRUCTURE    OF   -THE    TEETH,    THE    TONGUE,    AND    MUCOUS    MEMBRANE    OF 

THE    MOUTH, .  .         ]  49 

LESSON  XXIX. 

THE    SALIVARY    GLANDS, 161 

LESSON  XXX. 

THE   STRUCTURE    OF   THE   STOMACH, 167 

LESSONS  XXXI.  AND  XXXII. 

STRUCTURE    OF   SMALL   AND    LARGE    INTESTINE,  .  .  .  .  .173 

LESSON  XXXIII. 

STRUCTURE   OF   THE    LIVER   AND    PANCREAS, 181 

LESSON  XXXIV. 

STRUCTURE   OF   THE   SPLEEN,  SUPRARENAL   CAPSULE,  AND  THYROID    BODY,         187 

LESSON  XXXV. 

STRUCTURE    OF    THE    KIDNEY,     .........          192 

LESSON  XXXVI. 

STRUCTURE    OF   THE    URETER,    BLADDER,  AND    MALE    GENERATIVE  ORGANS,         200 

LESSON  XXXVII. 

GENERATIVE    ORGANS    OF    THE    FEMALE,    AND    MAMMARY    GLANDS,        .  .          209 

LESSON  XXXVIII. 

STRUCTURE    OF   THE   SPINAL   CORD, 216 

LESSONS  XXXIX.  AND  XL. 

THE   MEDULLA    OBLONGATA,    PONS   VAROLII,    AND    MESENCEPHALON,    .  .         227 


CONTENTS.  xi 

LESSON  XLI. 

PAOK 

STRUCTURE    OF    THE    CEREBELLUM    AND    CEREBRUM,  ....          241 

LESSONS  XLII.  AND  XLIII. 

STRUCTURE  OF  THE  EYELIDS  AND  OF  THE  PARTS  OF  THE  EYEBALL,     .    257 

LESSON  XLIV. 

STRUCTURE  OF  THE  OLFACTORY  MUCOUS  MEMBRANE  AND  OF  THE  EXTERNAL 

AND    MIDDLE   EAR, 276 

LESSON  XLV. 

STRUCTURE    OF    THE    LABYRINTH,          .  .  280 


APPENDIX. 

METHODS    USED    IN    PREPARING   SECTIONS, 290 

INDEX,  499 


THE  ESSENTIALS  OF  HISTOLOGY. 


INTRODUCTORY. 

ENUMERATION  OF  THE  TISSUES  AND  THE  GENERAL 
STRUCTURE  OF  ANIMAL  CELLS. 

Animal  Histology l  is  the  science  which  treats  of  the  minute  struc- 
ture of  the  tissues  and  organs  of  the  animal  body  ;  it  is  studied  with 
the  aid  of  the  microscope,  and  is  therefore  also  termed  Microscopical 
Anatomy. 

Every  part  or  organ  of  the  body,  when  separated  into  minute  frag- 
ments, or  when  examined  in  thin  slices  (sections),  is  found  to  consist  of 
certain  textures  or  tissues,  which  differ  in  their  arrangement  in  different 
organs,  but  each  of  which  exhibits  characteristic  structural  features. 

The  following  is  a  list  of  the  principal  tissues  which  compose  the  body  : — 

1.  Epithelial. 

2.  Connective  :  Areolar,  Fibrous,  Elastic,  Adipose,  Lymphoid,  Cartilage,  Bone. 

3.  Muscular:  Voluntary,  Involuntary  or  plain,  Cardiac. 

4.  Nervous. 

Some  organs  are  formed  of  several  of  the  above  tissues,  others  contain  only  one 
or  two. 

It  is  convenient  to  include  such  fluids  as  the  blood  and  lymph  amongst  the 
tissues,  because  they  are  studied  in  the  same  manner  and  contain  cellular  elements 
similar  to  those  met  with  in  some  of  the  other  tissues. 

The  elements  which  compose  the  tissues  are  of  the  nature  either 
of  fibres  or  cells.  Some  tissues  are  composed  almost  entirely  of  fibres 
with  relatively  few  cells  interspersed  amongst  the  fibres ;  this  is  the 
case  with  most  of  the  connective  tissues.  Others,  such  as  the  epithelial 
tissues,  are  composed  entirely  of  cells,  whilst  nervous  and  muscular 
tissues  are  formed  of  cells  which  are  partly  or  wholly  extended  to  form 
fibres. 

Cells. — A  cell  is  a  minute  portion  of  living  substance  or  protoplasm, 
which  is  sometimes  inclosed  by  a  cell-membrane  and  always  contains  a 
vesicle  which  is  known  as  the  nucleus. 

The  protoplasm  of  a  cell  (fig.  1,  p)  is  composed  of  albuminous  sub- 
stance, which  is  characterised  in  typical  cells  by  possessing  the  property 

1  From  torros,  a  web  or  texture. 
A 


THE  ESSENTIALS  OF  HISTOLOGY. 


FIG.  1.—  DIAGRAM  OP  A  CELL. 
toplasm  composed  of  spongio- 

and  hyaloplasm  ;  n,  nucleus 

with  intranuclear  network,  n'  ,  and 


of  spontaneous  movement.  When  the  cell  is  uninclosed  by  a  membrane 
a  change  in  the  shape,  or  even  in  the  position  of  the  cell,  may  be 
thereby  produced  (amoeboid  movement,  see  Lesson  V.).  The  proto- 
plasm often  exhibits  a  granular  appearance,  which,  under  high 
magnifying  powers,  is  seen  to  be  due  to  the  fact  that  it  is  composed 
of  two  distinct  substances  (fig.  1),  one  a  reticulum  or  sponge  work, 
which  appears  under  the  microscope  in  the  form  of  a  network,  and  the 
other  a  clear  soft  substance  which  occupies  the  interstices  of  the 
reticulum,  and  may  also  cover  the  surface  or  project  beyond  the  rest  of 

the  cell.  The  granular  appearance  above 
mentioned  is  caused  by  the  knots  in  the 

* 

network  appearing  when  imperfectly  ob- 
served as  separate  granules.  The  material 
which  forms  the  reticulum  is  termed  spong- 
ioplasm  ;  the  clear  material  which  occupies 
its  meshes  is  hyaloplasm.  The  protoplasm 
often  includes  actual  granules  of  albu- 
minous  or  fatty  nature,  or  globules  of 
watery  fluid  (vacuoles)  containing  glycogen 

,  ,,  .  ,       .  ,_-  ., 

or  other  substances  in  solution.  Materials 
which  are  thus  included  in  the  proto- 
plasm of  a  cell  are  either  stored  up  for  the  nutrition  of  the 
cell  itself,  or  are  converted  into  substances  which  are  eventually 
extruded  from  the  cell  in  order  to  serve  some  purpose  useful  to 
the  whole  organism,  such  as  the  secretion  which  is  furnished  by 
the  cells  of  a  gland.  The  term  paraplasm  has  been  given  by 
KupfFer  to  any  such  material  within  a  cell  other  than  the  actual 
protoplasm.  Paraplasm  is  often  present  in  sufficient  amount  to 
reduce  the  protoplasm  to  a  relatively  small  amount,  the  bulk  of  the  cell 
being  occupied  by  other  material,  as  when  starch  becomes  collected 
within  vegetable  cells  or  fat  within  the  cells  of  adipose  tissue.  In  some 
cells  there  are  fine  but  distinct  stria3  or  fibrils  running  in  definite 
directions.  These  are  very  commonly  met  with  in  fixed  cells,  such  as 
various  kinds  of  epithelium-cells,  nerve-  and  muscle-cells.  But  besides 
this  special  differentiation,  which  appears  to  be  related  to  the  special 
function  of  the  cell,  and  is  not  universal,  there  is  another  definite 
structure  in  the  cell-protoplasm,  which  is  known  as  the  attraction-sphere 
(fig.  2).  This  consists  of  a  wheel-like  arrangement  of  fine  fibrils  or  rows 
of  granules,  which  radiate  from  a  clear  area,  in  the  middle  of  which  lies  a 
central  particle  —  the  attraction-particle.  The  attraction-spheres  were 
discovered  by  v.  Beneden  in  the  ovum  or  egg-cell,  and  were  at  first 
supposed  to  be  peculiar  to  the  ovum,  but  they  have  now  been  recog- 


ANIMAL  CELLS.  3 

nised  (by  Flemming  and  others)  in  many  cells,  and  are  probably  of 
universal  occurrence.     They  are  very  often  double,  the  twin  spheres 


FIG.  2. — A  CELL  (WHITE  BLOOD  COK- 
PUSCLE)  SHOWING  ITS  ATTRACTION  - 

SPHEEE. 

In  this,  as  in  most  cases,  the  attraction- 
sphere  lies  near  the  nucleus. 


FIG.  3.— OVUM  OF  ASCARIS,  SHOWING 
A  TWIN  ATTRACTION-SPHERE.  (v. 
Beneden.) 

The  nucleus  with  its  contorted  filament 
of  chromoplasm  is  represented,  but  the 
protoplasm  of  the  cell  is  not  filled  in. 


being  connected  by  a  spindle-shaped  system  of  delicate  fibrils  (achro- 
matic spindle) :  this  duplication  invariably  precedes  the  division  of  a  cell 
into  two  (fig.  3). 

A  cell-membrane  is  rarely  distinct  in  animal  cells,  nor  has  its  chemical 
nature  been  sufficiently  investigated.  It  is  formed  by  the  external 
layer  of  the  protoplasm. 

The  nucleus  of  the  cell  (fig.  1,  n)  is  a  minute  vesicle,  spherical, 
ovoidal  or  elongated  in  shape,  embedded  in  the  protoplasm.  It  is 
bounded  by  a  membrane  which  incloses  a  clear  substance  (nuclear 
matrix),  and  the  whole  of  this  substance  is  generally  pervaded  by  an 
irregular  network  of  fibres,  some  coarser,  others  finer  (intranuclear  net- 
worlc).  This  intranuclear  network  often  exhibits  one  or  more  enlarge- 
ments, which  are  known  as  the  nudeoli.  The  nuclear  membrane, 
intranuclear  fibres  and  nucleoli  all  stain  deeply  with  haematoxylin  and 
with  most  other  dyes;  this  property  distinguishes  them  from  the 
nuclear  matrix,  and  they  are  accordingly  spoken  of  as  chromatic,  com- 
posed of  chromoplasm,  the  matrix  as  achromatic.  Sometimes  instead  of 
uniting  into  a  network  the  intranuclear  fibres  take  the  form  of  con- 
voluted filaments,  having  a  skein-like  appearance.  This  is  always  the 
case  when  a  nucleus  is  about  to  divide,  but  it  may  also  occur  in  the 
resting  condition.  These  filaments  may  sometimes  be  seen  with  very 
high  magnifying  powers  to  be  made  up  of  fine  juxtaposed  particles 
arranged  either  in  single  or  multiple  rows;  thus  imparting  a  cross- 
striated  appearance  to  the  filament  (see  fig.  4,  B,  c).  The  fibres  within 
the  nucleus  have  been  observed  to  undergo  spontaneous  changes  of 
form  and  arrangement,  but  these  become  much  more  evident  during 
its  division.  The  division  of  the  protoplasm  is  always  preceded  by 


4  THE  ESSENTIALS  OF  HISTOLOGY. 

that  of  the  nucleus,  and  the  intranuclear  fibres  undergo  during  its 
division  a  series  of  remarkable  changes  which  are  known  collectively 
by  the  term  karyokinesis  (Schleicher).  These  changes  may  most  easily 
be  studied  in  the  division  of  epithelium-cells  (see  Lesson  VI.),  but 
exactly  similar  phenomena  have  been  shown  to  occur  in  cells  belonging 
to  the  other  tissues. 


\. 


FlG.  4.  — TO  ILLUSTRATE  THE  STRUCTURE  OF  CELLS  AND  NUCLEI. 

A,  cell  from  the  marrow  ;  p,  protoplasm  with  fine  reticulum ;  n,  nucleus,  long  and  folded, 
with  intranuclear  network.  B,  gland  cell  from  a  larva  of  Nemocera  ;  m,  cell-membrane ; 
p,  protoplasm ;  n,  nucleus  with  convoluted  filament,  c,  part  of  the  nuclear  filament  in 
B,  greatly  magnified,  D,  an  amoaboid-cell  (white  blood-corpuscle)  of  the  newt,  very  highly 
magnified,  showing  a  double  nucleus  with  reticulum  of  chromoplasm,  and  the  protoplasm 
composed  of  two  substances  (spongioplasm  and  hyaloplasm).  D  is  from  a  drawing  by  Mr. 
D.  Gunn  ;  A,  B,  and  c  are  from  Carnoy. 

In  the  early  embryo  the  whole  body  is  an  agglomeration  of  cells.  These  have 
all  been  formed  from  the  ovum  or  egg-cell,  which  divides  first  into  two  cells,  these 
again  into  two,  and  so  on  until  a  large  number  of  cells  (embryonic  cells)  are  pro- 
duced. Eventually  the  resultant  cells  arrange  themselves  in  the  form  of  a  mem- 
brane (blastoderm)  which  is  composed  of  three  layers.  These  layers  are  known 
respectively  as  the  ectoderm  or  epiblast,  the  mesoderm  or  mesoblast,  and  the  entoderm 
or  hypoUast.  The  ectoderm  gives  rise  to  most  of  the  epithelial  tissues  and  the 
tissues  of  the  nervous  system  ;  the  entoderm  to  the  epithelium  of  the  alimentary 
canal  (except  the  mouth),  and  the  glands  in  connection  with  it;  and  the  mesoderm 
to  the  connective  and  muscular  tissues. 

The  tissues  are  formed  either  by  changes  which  occur  in  the  intercellular 
substance,  or  by  changes  in  the  cells  themselves  ;  frequently  by  both  these  pro- 


ANIMAL  CELLS. 


5 


Ectoderm 

or 
Epiblast. 


Mesoderm 

or 
Mesoblast. 


Entoderm 

or 
Hypoblast. 


The  epithelium  of  the  skin  or  epid 
sebaceous  and  sweat  glands. 


cesses  combined.  The  cells  which  are  least  altered  from  their  embryonic  condition 
are  the  white  corpuscles  of  the  blood,  and  these  may  be  regarded  therefore  as 
typical  cells. 

The  histogenetical  relation  between  the  three  layers  of  the  blastoderm  and  the 
several  tissues  and  organs  of  the  body  is  exhibited  in  the  following  table  : — 

ermis,  and  its  appendages,  viz.,  the  hairs,  nails, 

The  epithelium  of  the  mouth,  and  of  the  salivary  and  other  glands  which  open 
into  the  mouth.     The  enamel  of  the  teeth.     The  gustatory  organs. 

The  epithelium  of  the  nasal  passages,  and  the  cavities  and  glands  which  open 
into  them. 

The  epithelium  covering  the  front  of  the  eye.    The  cystalline  lens.    The  retina. 

The  epithelium  lining  the  membranous  labyrinth  of  the  ear. 

The  epithelium  lining  the  central  canal  of  the  spinal  cord,  the  aqueduct  of  Syl- 
vius, and  the  fourth,  third,  and  lateral  ventricles  of  the  brain. 

The  tissues  of  the  nervous  system. 
i^The  pituitary  body.    The  pineal  gland. 

The  connective  tissues. 
The  blood-  and  lymph-corpuscles. 

The  epithelial  lining  of  the  heart,  blood-vessels,  lymphatics,  and  serous  mem- 
branes (endothelium). 

The  epithelium  of  the  uriniferous  tubules. 

The  epithelium  of  the  generative  organs,  and  the  generative  products  in  both  sexes. 
The  muscular  tissues,  voluntary,  involuntary,  and  cardiac. 
The  spleen  and  other  lymphatic  and  vascular  glands. 

/The  epithelium  of  the  alimentary  canal  (from  the  pharynx  to  the  lower  end  of  the 
rectum)  and  all  the  glands  which  open  into  it  (including  the  liver  and 
pancreas). 
J  The  epithelium  of  the  Eustachian  tube  and  cavity  of  the  tympanum. 

I  The  epithelium  of  the  larynx,  trachea,  and  bronchi,  and  of  all  their  ramifications. 
The  epithelium  of  the  pulmonary  alveoli. 

I  The  epithelium  of  the  thyroid  body.  The  concentric  corpuscles  of  the  thymus  gland. 

*  The  epithelium  of  the  urinary  bladder. 


THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON    I. 

USE  OF  THE  MICROSCOPE.    EXAMINATION  OF 
COMMON  OBJECTS. 


THE  requisites  for  practical  Histology 
are  a  good  compound  microscope  ;  slips 
of  glass  technically  known  as  'slides,' 
upon  which  the  preparations  are  made  ; 
small  pieces  of  thin  glass  used  as  coA^ers 
for  the  preparations ;  a  few  simple  instru- 
ments, such  as  a  razor,  a  scalpel,  scissors, 
fine-pointed  forceps,  and  needles  mounted 
in  wooden  handles ;  and  a  set  of  fluid  re- 
agents for  mounting  and  staining  micro- 
scopic preparations.1  A  sketch-book  and 
pencil  are  also  necessary,  and  must  be 
constantly  employed. 

Examine  the  microscope  (fig.  5).  It 
consists  of  a  tube  (t  t')  having  two  systems 
of  lenses,  one  at  the  upper  end  termed 
the  '  eye-piece '  or  '  ocular '  (oc\  the  other 
at  the  lower  end,  termed  the  *  objective ' 
(obj\  There  should  be  at  least  two 
objectives — a  low  power  working  at  about 
^  inch  from  the  object,  and  a  high  power, 
having  a  focal  distance  of  about  ^  inch  ; 
and  it  is  also  useful  to  have  two  or  more 
oculars  of  different  power.  The  focus  is 
obtained  by  cautiously  bringing  the  tube 
and  lenses  down  towards  the  object  by 
the  coarse  adjustment,  which  is  either  a 
telescopic  or  a  rack-and-pinion  movement 
(adj\  and  focussing  exactly  by  the  fine 
adjustment,  which  is  always  a  finely  cut 
screw  {adj'), 

The  stage  (si)  upon  which  the  prepa- 
rations are  placed  for  examination,  the 
mirror  (m)  which  serves  to  reflect  the  light 
up  through  the  central  aperture  in  the 
stage  and  along  the  tube  of  the  instrument, 
and  the  diaphragm  (d)  below  the  stage 
which  is  used  to  regulate  the  amount  of 
light  thus  thrown  up,  are  all  parts  the 
employment  of  which  is  readily  under- 
stood. A  subetage  condenser  (not  shown 


EIG.  5. — DIAGRAM  OP  MICROSCOPE. 


1  The  directions  for  making  the  principal  fluids  used  in  histological  work  will  be  found 
in  the  Appendix. 


MICROSCOPICAL  EXAMINATION  OF  COMMON  OBJECTS.       7 

in  the  diagram),  which  serves  to  concentrate  the  light  thrown  up  by  the 
mirror  to  the  centre  of  the  object,  is  valuable  when  high  powers  and  stained 
preparations  are  employed. 

The  combinations  of  objectives  (•£  inch  and  J  inch  focal  distance)  and  oculars 
above  referred  to  will  generally  give  a  magnifying  power  of  from  50  to  400 
diameters,  and  this  is  sufficient  for  most  purposes  of  histology.  But  to  bring 
out  minute  points  of  detail  in  the  structure  of  cells  and  of  certain  tissues- 
examination  with  much  higher  magnifying  powers  may  be  necessary. 
Objectives  of  high  power  are  usually  made  as  immersion-lenses  ;  i.e.,  they 
are  constructed  to  form  a  proper  image  of  the  object  when  the  lowermost  lens 
of  the  system  is  immersed  in  a  layer  of  liquid  which  lies  on  the  cover-glass  of 
the  object  and  has  a  refractive  index  not  far  removed  from  that  of  the  glass 
itself.  For  this  purpose  either  water,  or  an  essential  oil  (e.g.  oil  of  cedar)  is 
used.  Many  advantages  are  obtained  by  the  employment  of  these  lenses, 
especially  those  for  oil-immersion. 

The  best  lenses  for  histological  work  are  those  which  are  made  of  the 
so-called  '  apochromatic '  glass  of  Zeiss  ;  with  these,  specially  constructed 
'compensating'  eye-pieces  are  used.  The  only  obstacle  to  their  general  use  is 
their  price. 

Prepare  a  scale  to  serve  for  measuring  objects  under  the  microscope.  To 
do  this  put  a  stage-micrometer  (which  is  a  glass  slide  ruled  in  the  centre,  with 
the  lines  YO  an<^  100  millimeter  apart)  under  the  microscope  in  such  a  manner 
that  the  lines  run  from  left  to  right  (the  microscope  must  not  be  inclined). 
Focus  them  exactly.  Put  a  piece  of  white  card  on  the  table  at  the  right  of 
the  microscope.  Look  through  the  instrument  with  the  left  eye,  keeping  the 
right  eye  open.  The  lines  of  the  micrometer  will  appear  projected  upon  the 
paper.  Mark  their  apparent  distance  with  pencil  upon  the  card,  and  after- 
wards make  a  scale  of  lines  in  ink  the  same  interval  apart.  A  magnified  re- 
presentation is  thus  obtained  of  the  micrometer-scale.  Mark  upon  it  the  num- 
ber of  the  eye-piece  and  of  the  objective,  and  the  length  of  the  microscope- 
tube.  This  scale-card  will  serve  for  the  measurement  of  any  object  without 
the  further  use  of  the  micrometer.  To  measure  an  object,  place  the  scale- 
card  upon  the  table  to  the  right  of  the  microscope  and  view  the  object  with 
the  left  eye,  keeping  the  right  eye  open.  The  object  appears  projected  upon 
the  scale,  and  its  size  in  ^  or  y^  of  a  millimeter  can  be  read  off.  It  is 
important  that  the  same  objective  and  eye-piece  should  be  employed  as  were 
used  in  making  the  scale,  and  that  the  microscope-tube  should  be  of  the  same 
length.  The  lines  on  the  English  stage-micrometers  are  usually  ruled  y^ 
and  YO^OU  illch  apart.1 

Before  beginning  the  study  of  histology  the  student  should  endeavour  to 
familiarise  himself  with  the  use  of  the  microscope,  and  at  the  same  time 
learn  to  recognise  some  of  the  chief  objects  which  are  liable  to  occur 
accidentally  in  microscopic  specimens.  On  this  account  it  has  been  considered 
desirable  to  introduce  directions  for  the  examination  of  starch-granules, 
moulds  and  torulse,  air-bubbles,  linen,  cotton,  and  woollen  fibres,  and  the 
usual  constituents  of  the  dust  of  a  room,  into  the  first  practical  lesson. 

1.  Examination  of  starch-granules.  Gently  scrape  the  cut  surface  of  a 
potato  with  the  point  of  a  knife  ;  shake  the  starch-granules  so  obtained  into 
a  drop  of  water  upon  a  clean  slide  and  apply  a  cover-glass. 

With  the  low  power  the  starch-granules  look  like  dark  specks  differing 
considerably  in  size ;  under  the  high  power  they  are  clear,  flat,  ovoid  particles 
(fig.  6,  St),  with  a  sharp  outline  when  exactly  focussed.  Notice  the  change  in 
appearance  of  the  outline  as  the  microscope  is  focussed  up  or  down.  On  close 
examination  fine  concentric  lines  are  to  be  seen  in  the  granules  arranged 

1  For  the  method  of  measuring  with  an  ocular  micrometer,  and  for  determining 
the  magnifying  power  of  a  microscope,  the  student  is  referred  to  the  author's  Course  of 
Practical  Histology. 


8  THE  ESSENTIALS  OF  HISTOLOGY. 

around  a  minute  spot  which  is  generally  placed  eccentrically  near  the  smaller 
end  of  the  granule.     Sketch  two  or  three  starch-granules. 

Notice   the   appearance   of  air-bubbles   in  the  water.     If  comparatively 


FIG.  6.— ORGANIC  MATTERS  FREQUENTLY  PRESENT  IN  DUST.    (Heitzmann.) 

S,  fibres  of  silk  ;  C,  of  cotton  ;  L,  of  linen  ;  W,  of  wool ;  F,  feather  ;  St,  starch -granules  ;  Cr, 
cork ;  0,  torulae  ;  M,  mycelium  or  threads  of  mildew ;  Me,  micrococci ;  B,  bacteria ;  Lt, 
leptothrix  filaments  (500  diameters). 

large  they  are  clear  in  the  middle,  with  a  broad  dark  border  due  to  refraction 
of  the  light ;  if  small  they  may  look  entirely  dark. 

2.  Examine  some  brewers'  yeast  which  has  been  grown  in  solution  of 
sugar.  Observe  the  yeast-particles  or  torulse,  some  of  them  budding.  Each 
torula  contains  a  clear  vacuole,  and  has  a  well-defined  outline,  due  to  a 
membrane.  Sketch  two  or  three  torulse. 


MICEOSCOPICAL  EXAMINATION  OF  COMMON  OBJECTS.       9 

3.  Examine  some  mould  (Peiricillium  or  Mucor)  in  water.     Notice  the  long 
branching  filaments  (hyphse),  and  also  the  torula-like  particles  (spores)  from 
which  hyphae  may  in  some  instances  be  seen  sprouting.      Sketch  part  of  a 
hypha. 

4.  Examine  fibres  of  linen,  and  of  cotton  in  water,  using  a  high  power. 
Compare  the  well-defined,  relatively  coarse,  striated,  and  slightly  twisted 
linen,  with  the  longer,  thinner,  and  more  twisted  cotton-fibres.     Sketch  one 
of  each  kind. 

5.  Mount  two  or  three  hairs  from  the  head  in  water  and  look  at  them, 
first  with  the  low,  then  with  the  high  power.     Examine  also  some   fibres 
from  any  woollen  material  and  compare  them  with  the  hairs.     They  have 
the  same  structure,  although  the  wool  is  finer  and  is  curled  ;  its  structure 
may  be  partly  obscured  by  the  dye.     Draw  one  or  two  woollen  fibres. 

6.  Examine   some   dust   of   the  room    in   water  with  a  high  power.     In 
addition  to  numerous  groups  of  black  particles  of  carbon  (soot)  there  will 
probably  be  seen  fibres  of  linen,  cotton,  or  wool,  and  shed  epithelium-cells 
derived  from  the  epidermis. 


10  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  II. 

STUDY  OF  THE  HUMAN  BLOOD-CORPUSCLES. 

1.  HAVING  cleaned  a  slide  and  cover-glass,  prick  the  finger  and  mount  a 
small  drop  of  blood  quickly,  so  that  it  has  time  neither  to  dry  nor  to 
coagulate.  Examine  it  at  once  with  the  high  power. 

Note  (a)  the  coloured  corpuscles,  mostly  in  rouleaux  and  clumps,  but  some 
lying  apart  seen  flat  or  in  profile  ;  (6)  the  colourless  corpuscles,  easily  made 
out  if  the  cover-glass  is  touched  by  a  needle,  on  account  of  their  tendency  to 
stick  to  the  glass,  whilst  the  coloured  corpuscles  are  driven  past  by  the  cur- 
rents set  up  ;  (c)  in  the  clear  spaces,  fibrin-filaments  and  elementary  particles 
or  blood-tablets. 

Sketch  a  roll  of  coloured  corpuscles  and  one  or  two  colourless  corpuscles. 
Count  the  number  of  colourless  corpuscles  in  a  field  of  the  microscope. 

2.  To  be  made  like  1,  but  the  drop  of  blood  ifc  to  be  mixed  upon  the  slide 
with  an  equal  amount  of  normal  saline  solution,1  so  that  the  red  corpuscles 
tend  to  be  less  massed  together,  and  their  peculiar  shape  is  better  displayed. 

Sketch  a  red  corpuscle  seen  on  the  flat  and  another  in  profile  (or  optical 
section).  Also  a  crenated  corpuscle. 

Measure  ten  red  corpuscles,  and  from  the  results  ascertain  the  average 
diameter  of  a  corpuscle.  Measure  also  the  largest  and  the  smallest  you 
can  find. 

3.  Make  a  preparation  of  blood  as  in  §  1  and  put  it  aside  to  coagulate. 
After  fifteen  minutes  allow  a  drop  of  a  strong  solution  of  neutral  carminate 
of  ammonia  to  run  under  the  cover-glass.    This  decolorises  the  red  corpuscles, 
but  stains  the  nuclei  of  the  white  corpuscles  and  brings  the  network  of  fibrin- 
filaments  and  the  elementary  particles  clearly  into  view  (fig.  10,  A).     When 
the  fibrin  is  fully  stained,  a  drop  of  glycerine  is  allowed  to  diffuse  into  the 
fluid.     The  cover-glass  may  then  be  cemented  with  gold-size  and  the  pre- 
paration labelled  and  kept. 

4.  Enumeration  of  the  blood-corpuscles.     This  is  done  by  some  form  of 
blood-counter  such  as  the  hsemacytometer  of  Gowers.     This  instrument  con- 
sists of  a  glass  slide  (fig.  7,  c),  the  centre  of  which  is  ruled  into  ^  millimeter 
squares  and  surrounded  by  a  glass  ring  i  mm.  thick.     It  is  provided  with 
measuring  pipettes  (A  and  B),  a  vessel  (D)  for  mixing  the  blood  with  a  saline 
solution   (sulphate  of  soda  of  sp.  gr.  1015),  glass  stirrer  (E)  and  guarded 
needle  (F). 

995  cubic  millimeters  of  the  saline  solution  are  placed  in  the  mixing  jar ; 
5  cubic  millimeters  of  blood  are  then  drawn  from  a  puncture  in  the  finger 
and  blown  into  the  solution.  The  two  fluids  are  well  mixed  by  the  stirrer 
and  a  small  drop  of  this  dilution  (1  to  200)  is  placed  in  the  centre  of  the  cell, 
the  cover-glass  gently  laid  on  (so  as  to  touch  the  drop,  which  thus  forms  a 
layer  i  mm.  thick  between  the  slide  and  cover-glass)  and  pressed  down  by 
two  brass  springs.  In  a  few  minutes  the  corpuscles  have  sunk  to  the  bottom 
of  the  layer  of  fluid  and  rest  on  the  squares.  The  number  in  ten  squares  is 
then  counted,  and  this,  multiplied  by  50  gives  the  number  in  a  cubic  milli- 

1  Made  by  dissolving  6  grammes  of  common  salt  in  1  litre  of  ordinary  water. 


STUDY  OF  THE  HUMAN  BLOOD-CORPUSCLES. 


11 


meter  of  the  mixture,  or  if  multiplied  by  50  x  200  (  =  10,000)  the  number  in  a 
cubic  millimeter  of  blood  is  obtained. 


FlG.  7.— H^MACYTOMETER  OF   GOWERS. 


FIG.  8.— HUMAN  BLOOD  AS  SEEN  ON  THE  WARM        FIG.    9.— HUMAN    RED    CORPUS- 


STAGE.  (Magnified  about  1200  diameters. ) 
,  r,  single  red  corpuscles  seen  lying  flat ;  /,  r',  red  cor- 
puscles on  their  edge  and  viewed  in  profile;  r",  red 
corpuscles  arranged  in  rouleaux ;  c,  c,  crenate  red  cor- 
puscles ;  p,  a  finely  granular  pale  corpuscle ;  g,  a 
coarsely  granular  pale  corpuscle.  Both  have  two  or 
three  distinct  vacuoles,  and  were  undergoing  changes 
of  shape  at  the  moment  of  observation  ;  in  g,  a  nucleus 
also  is  visible. 


CLES   LYING  SINGLY   AND    COL- 
LECTED INTO  ROLLS.     (As  seen 
under  an  ordinary  high  power 
of  the  microscope.) 
1,  On  the  flat ;  S,  in  profile. 


12 


THE  ESSENTIALS  OF  HISTOLOGY. 


The  coloured  blood-corpuscles. — Under  the  microscope  the  blood  is 
seen  to  consist  of  a  clear  fluid  (plasma),  in  which  are  suspended  the 
blood-corpuscles.  The  latter  are  of  two  kinds  :  the  red  or  coloured  (fig.  8, 
r,  r),  which  are  by  far  the  most  numerous,  and  the  white,  pale,  or 
colourless  (p,  g),  which  from  their  occurrence  in  the  lymph  are  also 
known  as  lymph-cwpuscles.  When  seen  singly  the  coloured  corpuscles 
are  not  distinctly  red,  but  appear  of  a  reddish-yellow  tinge.  In  the 
blood  of  man  and  of  all  other  mammals,  except  the  Camelidae,  they 
are  biconcave  circular  disks.  Their  central  part  usually  has  a  lightly 
shaded  aspect,  under  the  ordinary  high  power  (fig.  9,  1),  but  this  is  due 
to  their  biconcave  shape,  not  to  the  presence  of  a  nucleus.  They  have 
a  strong  tendency  to  become  aggregated  into  rouleaux  and  clumps 
when  the  blood  is  at  rest,  but  if  it  is  disturbed  they  readily  become 
separated. 

If  the  density  of  the  plasma  is  increased  in  any  way,  as  by  evapora- 
tion, many  of  the  red  corpuscles  become  shrunken  or  crenated  (c). 

The  average  diameter  of  the  human  red  corpuscles  is  0'0075  milli- 
meter (about  ^Vir  inch).1 

There  are  from  four  to  five  millions  of  coloured  corpuscles  in  a  cubic 
millimeter  of  blood. 

The  colourless  corpuscles  of  human  blood  are  protoplasmic  cells, 
averaging  0*01  mm.  (^-Vo^  incn)  in  diameter  when  spheroidal,  but  they 

vary  much  in  size.  They  are  far 
fewer  than  the  coloured  corpuscles, 
usually  numbering  not  more  than 
ten  thousand  in  a  cubic  millimeter. 
Moreover,  they  are  specifically 
lighter,  and  tend  to  come  to  the 
surface  of  the  preparation.  If  ex- 
amined immediately  the  blood  is 
drawn,  they  are  spheroidal  in  shape, 
but  they  soon  become  irregular 
FIG.  10.— FIBRIN-FILAMENTS  AND  BLOOD-  (fig.  8,  p,  g),  and  their  outline  con- 
TABLETS.  tinually  alters,  owing  to  the  amboea- 

A,  network  of  fibrin,  shown  after  washing  away  .....          ..  _  ,  .   ,        , 

the  corpuscles  from  a  preparation  of  blood  like  changes    01  lOrni  to  Which    they 
that  has  been  allowed  to  clot ;  many  of  the  ,  .  „  A ,  ,         , 

filaments  radiate  from  small  clumps  of  blood-  are  SUDJCCt.      bome  OI  the  COlOUriCSS 
tablets.     B  (from  Osier),  blood-corpuscles  and  -,  j     ~    '   -. 

elementary  particles  or  blood-tablets,  within  Corpuscles    are  Very  pale   and    finely 

granular,  others  contain  coarser  and 
more  distinct  granules  in  their  protoplasm.     The  protoplasm  may  also 

1  The  following  list  gives  the  diameter  in  parts  of  -A  millimeter  of  the  red  blood- 
corpuscles  of  some  of  the  common  domestic  animals: — Dog,  0'0073;  rabbit,  0'0069; 
cat,  0-0065  ;  sheep,  0'0050  ;  goat,  0'0041. 


COLOURLESS  CORPUSCLES.  1  3 

contain  clear  spaces  or  vacuoles,  and  it  has  a  reticular  structure.  Each 
pale  corpuscle  has  one  or  more  nuclei,  which  are  difficult  to  see  without 
the  aid  of  reagents. 

In  the  clear  fluid  in  which  the  corpuscles  are  suspended,  a  network 
of  fine  straight  intercrossing  filaments  (fibrin)  soon  makes  its  appearance 
(fig.  10,  A).  There  are  also  to  be  seen  a  certain  number  of  minute 
round  colourless  discoid  particles,  either  separate  or  collected  into  groups 
or  masses,  which  may  be  of  considerable  size.  These  are  the  elementary 
particles  or  blood-tablets.  Their  meaning  is  not  known.  Fatty  particles, 
derived  from  the  chyle,  may  also  occur  in  the  plasma. 

Development  of  blood-corpuscles. — In  the  embryo,  the  first-formed 
coloured  blood-corpuscles  are  amoeboid  nucleated  cells,  the  protoplasm  of 


FIG.  11.— DEVELOPMENT  OF  BLOOD-VESSELS  AND  BLOOD-CORPUSCLES  IN  THE  VASCULAR 
AREA  OF  THE  GUINEA-PIG. 

l>l,  blood-corpuscles  becoming  free  in  the  interior  of  a  nucleated  protoplasmic  mass. 

which  contains  haemoglobin.  These  embryonic  blood-corpuscles  are 
developed  within  cells  of  the  mesoblast,  which  are  united  with  one 
another  to  form  a  protoplasmic  network  (fig.  11).  The  nuclei  of  the 
cells  multiply,  and  around  some  of  them  there  occurs  an  aggregation  of 
coloured  protoplasm.  Finally  the  network  becomes  hollowed  out  by  an 
accumulation  of  fluid  in  the  protoplasm,  and  thus  are  produced  a  num- 
ber of  capillary  blood-vessels,  and  the  coloured  nucleated  portions  of 
protoplasm  are  set  free  within  them  as  the  embryonic  blood-corpuscles 
(fig.  11,  bl). 

In  later  embryonic  life,  nucleated  coloured  corpuscles  disappear  from 
mammalian  blood,  and  are  replaced  by  the  usual  discoid  corpuscles. 
These  are  formed  within  certain  cells  of  the  connective  tissue,  a  portion 
of  the  substance  of  the  cell  becoming  coloured  by  haemoglobin,  and 
separated  into  globular  particles  (fig.  12,  a,  b,  c),  which  are  gradually 
moulded  into  disk-shaped  red  corpuscles.  In  the  meantime  the  cells 


14 


THE  ESSENTIALS  OF  HISTOLOGY. 


become  hollowed  out,  and  join  with  similar  neighbouring  cells  to  form 
blood-vessels  (fig.  13,  a,  b,  c).  The  process  is  therefore  the  same  as 
before,  except  that  the  cell-nuclei  do  not  participate  in  it. 

Although  no  nucleated  coloured  corpuscles  are  to  be  seen  in  the 
blood  in  post-embryonic  life,  they  continue  to  be  formed  in  the  marrow 
of  the  bones  (see  Lesson  XIII. ),  and  in  some  animals  they  have  also 
been  found  in  the  spleen.  It  is  thought  probable  that  the  red  disks 
may  be  formed  from  these  by  the  nucleus  disappearing  and  the  coloured 
protoplasm  becoming  moulded  into  a  discoid  shape.  Others  have  sup- 


FIG.  12. — BLOOD-CORPUSCLES  DEVELOPING  WITHIN  CONNECTIVE-TISSUE  CELLS. 

a,  a  cell  containing  diffused  haemoglobin  ;  6,  a  cell  filled  with  coloured  globules  ;  c,  a  cell  con- 
taining coloured  globules  in  the  protoplasm,  within  which  also  are  numerous  vacuoles. 

posed  that  the  red  disks  are  derived  from  the  white  corpuscles  of  the 
blood  and  lymph,  and  others  again  that  they  are  developed  from  the 
blood-tablets ;  but  the  evidence  in  favour  of  these  views  is  insufficient. 
The    white  blood-corpuscles   and   lymph-corpuscles  occur   originally   as 


FIG.  13. — FURTHER  DEVELOPMENT  OF 
BLOOD-CORPUSCLES  IN  CONNECTIVE- 
TISSUE  CELLS,  AND  TRANSFORMA- 
TION OF  THE  LATTER  INTO  CAPIL- 
LARY BLOOD-VESSELS. 

«.,  an  elongated  cell  with  a  cavity  in  its 
protoplasm  occupied  by  fluid  and  by 
blood-corpuscles  mostly  globular ;  6,  a 
hollow  cell  the  nucleus  of  which  has 
multiplied.  The  new  nuclei  are 
arranged  around  the  wall  of  the 
cavity,  the  corpuscles  in  which  have 
now  become  discoid;  c  shows  the 
mode  of  union  of  a  '  haemapoietic '  cell, 
which  in  this  instance  contains  only 
one  corpuscle,  with  the  prolongation 
(bl)  of  a  previously  existing  vessel,  a, 
and  c,  from  the  new-born  rat ;  &,  from 
a  foatal  sheep. 


free  unaltered  embryonic  cells,  which  have  found  their  way  into  the 
vessels  from  the  circumjacent  mesoblast.  Later  they  become  formed 
in  lymphatic  glands  and  other  organs  composed  of  lymphoid  tissue, 
and  pass  from  these  directly  into  the  lymphatics  and  so  into  the  blood. 


HUMAN  BLOOD-COEPUSCLES.  15 


LESSON  III. 

ACTION  OF  REAGENTS  UPON  THE  HUMAN  BLOOD- 
CORPUSCLES. 

1.  MAKE  a  preparation  of  blood  as  in  Lesson  II.  1,  and  apply  a  drop  of  water 
at  one  edge  of  the  cover-glass.  Examine  at  a  place  where  the  two  fluids  are 
becoming  mixed.  Notice  particularly  the  first  effect  of  water  upon  both  red 
and  white  corpuscles,  as  well  as  the  ultimate  action. 

Sketch  both  kinds  of  corpuscles  under  the  action  of  water. 

2.  Eepeat  on  another  preparation,  using  very  dilute  alkali  (0'2  per  cent, 
potash  in  salt  solution)  instead  of  water.     Notice  the  complete  solution  first 
of  the  white  and  then  of  the  coloured  corpuscles  as  the  alkali  reaches  them. 

3.  Eepeat  on  another  preparation,  using  dilute  acetic  acid  (1  per  cent.). 
Observe  that  the  effect  of  the  acid  upon  the  coloured  corpuscles  is  similar  to 
that  of  water,  but  that  it  has  a  different  action  upon  the  colourless  corpuscles. 

Sketch  two  or  three  of  the  latter  after  the  action  is  completed. 

4.  Make  a  preparation  of  blood  mixed  with  salt  solution  as  in  Lesson  II.  2, 
and  investigate  the  action  of  tannic  acid  (1  part  tannic  acid  to  1000  of  dis- 
tilled water)  in  the  same  way. 

Sketch  two  or  three  coloured  corpuscles  after  the  reaction  is  complete. 


The  action  of  reagents  upon  the  human  red  blood-corpuscles  shows 
that,  although  to  all  appearance  homogeneous,  they  in  reality  consist 
of  an  external  envelope  of  colourless  material    a        &         <*        <l       e 
which  forms  a  thin  film  enclosing  the  dis- 
solved  colouring  matter  or  Ticemoglobin.    Thus, 
when  water  reaches  the  corpuscle,  it  passes 
through  the  film  by  osmosis  and  swells  the 
corpuscle,    causing   it   to   become   globular ;  FlG  14 

eventually  the  film  is  burst  through,  and  the  a.c>  successive  effects  of  water  upon 
colouring  matter  escapes  into  the  serum.  LiutnXsaiV;  i  SKt  $ 
Salt,  on  the  other  hand,  by  increasing  the  tannicacid- 
density  of  the  fluid  in  which  the  corpuscles  float,  causes  a  diffusion  of 
water  out  of  the  corpuscle,  and  a  consequent  shrinking  and  corrugation 
of  the  surface,  the  crenated  form  (fig.  8,  c ;  fig.  1 4,  /)  being  thereby 
produced.  The  separation  of  the  haemoglobin  from  the  corpuscle  can 
be  effected  not  only  by  water  (fig.  14,  a-e),  but  also  by  dilute  acids,  by 
the  action  of  heat  (60°  C.),  the  freezing  and  thawing  of  blood,  the 
vapour  of  chloroform,  and  the  passage  of  electric  shocks  through 


16  THE  ESSENTIALS  OF  HISTOLOGY. 

blood.1  The  mixing  of  human  blood  with  the  blood  or  serum  of  various 
animals  also  has  a  similar  action,  probably  owing  to  differences  of 
density  or  alkalinity.  Tannic  acid  produces  a  peculiar  effect  (fig.  14,  g); 
the  haemoglobin  is  discharged  from  the  corpuscle,  but  is  immediately 
altered  and  precipitated,  remaining  adherent  to  the  envelope  in  the 
form  of  a  round  or  irregular  globule  of  a  brownish  tinge  (hematin  ?). 

Some  of  these  reactions  occur  by  process  of  osmosis  as  in  the  case  of  water, 
but  in  others  a  physical  or  chemical  solution  of  the  envelope  of  the  corpuscle 
is  produced,  and  the  haemoglobin  is  thus  allowed  to  escape.  The  film  or 
envelope  is  probably  in  large  measure  composed  of  lecithin  and  cholesterin 
(along  with  a  little  cell-globulin — Halliburton),  and  these  are  substances 
which  possess  many  of  the  physical  properties  of  fats,  although  of  a  different 
chemical  composition.  If  we  assume  this  to  be  its  composition  the  running 
of  the  red  disks  into  rouleaux  can  readily  be  explained,  since  it  has  been 
shown  by  Norris  that  disks  of  any  material,  e.g.  cork,  floating  in  a  fluid,  tend 
in  the  same  way  to  adhere  in  rouleaux,  provided  their  surfaces  are  covered 
with  a  layer  which  is  not  wetted  by  the  fluid. 

The  envelope  of  the  red  corpuscle  is  often  termed  the  stroma  (Eollett),  but 
this  name  rests  upon  an  entirely  false  conception  of  the  structure  of  the  cor- 
puscle, and  although  of  late  years  almost  universally  used,  it  ought  to  be 
entirely  abandoned.  In  adopting  the  name,  it  was  supposed  that  the  corpuscle 
is  formed  of  a  homogeneous  porous  material  (stroma),  in  the  pores  of  which 
the  haemoglobin  is  contained,  but  there  is  no  reasonable  foundation  for  this 
belief,  whereas  the  supposition  that  there  exists  a  delicate  external  film  or 
envelope  inclosing  a  coloured  fluid  is  in  accordance  with  all  the  known  facts 
regarding  the  action  of  reagents  upon  these  bodies. 

The  structure  of  the  colourless  corpuscles  is  also  brought  out  by 
the  action  of  some  of  these  reagents.  As  the  water  reaches  them  their 
amoeboid  movements  cease ;  they  become  swollen  out  into  a  globular 


FIG.  15. 

1.  first  effect  of  the  action  of  water  upon  a  white  blood  corpuscle:  2,  3,  white  corpuscles 
treated  with  dilute  acetic  acid  ;  n,  nucleus. 

form  by  imbibition  of  fluid  (fig.  15,  1),  and  the  granules  within  the 
protoplasm  can  be  seen  to  be  in  active  Brownian  motion.  Their  nuclei 
also  become  clear  and  globular,  and  are  more  conspicuous  than  before. 

1  In  the  blood  of  some  animals  crystals  of  haemoglobin  readily  form  after  its 
separation  by  any  of  these  means  from  the  red  corpuscles.  These  crystals  are 
rhombic  prisms  in  most  animals,  but  tetrahedra  in  the  guinea-pig,  and  hexagonal 
plates  in  the  squirrel.  They  are  most  appropriately  studied  along  with  the 
chemical  and  physical  properties  of  blood,  and  are  therefore  omitted  here.  The 
same  remark  applies  to  the  minute  dark-brown  rhombic  crystals  (hcemin),  which 
are  found  when  dried  blood  is  heated  with  glacial  acetic  acid,  and  to  the  reddish- 
yellow  crystals  of  hcematoiditt,  which  are  found  in  old  blood  extravasations. 


COLOURLESS  CORPUSCLES.  17 

With  the  further  action  of  the  water,  the  corpuscle  bursts  and  the 
granules  are  set  free. 

Acids  have  an  entirely  different  action  upon  the  white  corpuscles. 
Their  nuclei  become  somewhat  shrunken  and  very  distinct  (fig.  15, 
2  and  3),  and  a  granular  precipitate  is  formed  in  the  protoplasm  around 
the  nucleus.  At  the  same  time,  a  part  of  the  protoplasm  generally 
swells  out  so  as  to  form  a  clear  bleb-like  expansion  (an  appearance 
which  often  accompanies  the  death  of  the  corpuscle  from  other  causes). 


18  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  IV. 

STUDY  OF  THE  BLOOD-CORPUSCLES  OF  AMPHIBIA. 

1.  MOUNT  a  drop  of  newt's  blood  obtained  from  the  cut  end  of  the  tail.  It 
may  be  allowed  to  mix  with  a  very  small  quantity  of  salt  solution.  Examine 
with  the  high  power.  Notice  the  shape  of  the  coloured  corpuscles  both  when 
seen  flat  and  edgeways,  and  the  nucleus  within  each. 

Measure  ten  corpuscles  (long  and  short  diameters),  and  from  the  results 
obtain  the  average  dimensions  of  the  newt's  blood-corpuscle. 

Notice  also  the  colourless  corpuscles,  smaller  than  the  red,  but  considerably 
larger  than  the  pale  corpuscles  of  human  blood,  although  otherwise  resembling 
these. 

Sketch  two  or  three  red  corpuscles  and  as  many  white. 

Be  careful  not  to  mistake  the  liberated  nuclei  of  crushed  red  corpuscles  for 
pale  corpuscles. 

Enormous  cells  and  nuclei  belonging  to  the  cutaneous  glands  as  well  as  the 
granular  secretion  of  those  glands  may  be  present  in  this  preparation. 

2.  Apply  a  drop  of  water  to  the  edge  of  the  cover-glass  of  the  same  pre- 
paration and  notice  its  action  upon  the  corpuscles. 

Sketch  two  or  three  corpuscles  altered  by  the  action  of  the  water. 

3.  Mount  another  drop  of  blood,  and  apply  dilute  acetic  acid  (1  per  cent.) 
instead  of  water  at  the  edge  of  the  cover-glass.     Make  sketches  showing  the 
effect  of  the  acid  upon  both  red  and  white  corpuscles. 

4.  Examine  the  corpuscles  of  newt's  blood  which  has  been  allowed  to  flow 
into  boracic  acid  solution  (2  per  cent.).     Notice  the  effect  produced  upon  the 
coloured  corpuscles.     Sketch  one  or  two. 


The  coloured  blood-corpuscles  of  amphibia  (fig.  16),  as  well  as  of 
most  vertebrates  below  mammals,  are  biconvex  elliptical  disks,  consider- 
ably larger  than  the  biconcave  circular  disks  of  mammals.1  In  addition 
to  the  coloured  body  of  the  corpuscle,  which  consists,  as  in  mammals,  of 
haemoglobin  inclosed  within  an  envelope,  there  is  a  colourless  nucleus, 
also  of  an  elliptical  shape,  but  easily  becoming  globular,  especially  if 
liberated  by  any  means  from  the  corpuscle.  The  nucleus  resembles 

1  The  following  are  the  dimensions  in  parts  of  a  millimeter  of  some  of  the  cor- 
puscles of  oviparous  vertebrates  : — 

Long  diameter  Short  diameter 

Pigeon         .         .         .  0-0147  0'0065 


Frog   . 
Newt . 
Proteus 
Amphmma . 


0-0223  0-0157 

0-0293  0-0195 

0-058  0-035 

0-077  0-046 


COLOUEED  BLOOD-COEPUSCLES  OF  AMPHIBIA. 


19 


that  of  other  cells  in  structure,  being  bounded  by  a  membrane,  and 
having  a  network  of  filaments  traversing  its  interior  (fig.  17).  It  is  not 
very  distinct  in  the  unaltered  corpuscle,  but  is  brought  clearly  into 
view  by  the  action  of  reagents,  especially  acetic  acid.  The  action  of 
reagents  upon  the  red  corpuscle  of  amphibia  is  otherwise  similar  to  that 
produced  upon  the  mammalian  corpuscle,  water  and  acetic  acid  causing 


FIG.  17. — COLOURED 
CORPUSCLE  OP  SA- 
LAMANDER, SHOW- 
ING INTRANUCLEAR 

NETWORK.      (Flem- 

ming.) 

FIG.  16.— FROG'S  BLOOD.     (Ranvier.) 

a,  red  corpuscle  seen  on  the  flat ;  v,  vacuoles  in  a  cor- 
puscle ;  b,  c,  red  corpuscles  in  profile ;  k,  n,  pale  cor- 
puscles at  rest ;  m,  pale  corpuscle  exhibiting  amoe- 
boid movements ;  p,  colourless  fusiform  corpuscle. 

it  to  swell  into  a  globular  form  and  then  to  become  decolorised ;  solu- 
tion of  salt  causing  wrinkling  of  the  envelope,  and  so  on.  Boracic  acid 
acts  like  tannic  acid  in  causing  the  haemoglobin  to  be  withdrawn  from 
the  envelope ;  but  it  becomes  partially  or  wholly  collected  around  the 
nucleus,  which  may  then  be  extruded  from  the  corpuscle. 

The  colourless  corpuscles  (fig.  16,  Jc,  m,  n),  although  larger,  are  very 
similar  to  those  of  mammals.  Like  them,  they  are  either  wholly  pale 
or  inclose  a  number  of  dark  granules.  They  vary  much  in  size  and  in 
the  activity  of  their  amoeboid  movements.  They  may  have  one  or 
several  nuclei.  Keagents  have  the  same  effect  upon  them  as  on  those 
of  mammals.  The  presence  of  glycogen  may  be  demonstrated  in  them 
by  its  reaction  with  iodine  (port-wine  colour). 


THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  V. 


THE  AMCEBOID  PHENOMENA  OF  THE  COLOURLESS 
BLOOD-CO  RP  USCLES. 

1.  MAKE  a  preparation  of  blood  from  the  finger  in  the  usual  way.  Draw 
a  brush  just  moistened  with  oil  around  the  edge  of  the  cover-glass  to  check 
evaporation.  Place  the  preparation  upon  a  '  warm  stage/  and  heat  this  to 
about  the  temperature  of  the  body  (38°  C).  Bring  a  white  corpuscle  under 
observation  with  the  high  power,  and  watch  the  changes  of  shape  which  it 
undergoes.  To  become  convinced  of  these  alterations  in  form,  make  a  series 
of  outline  sketches  of  the  same  corpuscle  at  intervals  of  a  minute. 

The  simplest  form  of  '  warm  stage '  is  a  copper  plate  of  about  the  size  of 
an  ordinary  slide,  perforated  in  the  centre  and  with  a  long  tongue  of  the  same 


FIG.  18.— SIMPLE  WARMING  APPARATUS,  COMPLETE,  SHOWN  IN  OPERATION. 

metal  projecting  from  the  middle  of  one  edge  (fig.  18).  The  copper  plate 
rests  upon  the  stage  of  the  microscope  with  a  piece  of  cloth  or  other  non- 
conducting material  between.  The  preparation  is  made  upon  an  ordinary 
slide,  which  is  placed  upon  the  warm  stage  and  pressed  into  contact  with 


AMCEBOID  PHENOMENA. 


21 


it  by  the  brass  clips.  Heat  is  applied  to  the  copper  tongue  by  a  small  spirit- 
lamp  flame,  and  a  greater  or  less  amount  is  conducted  to  the  warm  stage 
and  the  superjacent  preparation  according  to  the  point  to  which  the  flame  is 
applied.  To  ascertain  that  the  right  temperature  is  got  and  maintained,  put 
two  pieces  of  paraffin,  one  melting  at  35°  C.  (95  F.)  and  another  at  38°  C. 
(100°  F.),  on  the  slide,  one  011  either  side  of  the  preparation.  The  tempera- 
ture must  be  such  that  the  first  piece  is  melted  and  remains  so  whilst  the 
second  remains  solid.1 

2,  Mount  a  drop  of  newt's  blood  diluted  with  an  equal  amount  of  salt 
solution,  and  examine  it  in  the  same  manner  upon  the  copper  stage,  at  first 
cold,  afterwards  warm  ;  the  temperature  must,  however,  be  kept  below  30°  C. 
Observe  the  effect  of  heat  in  accelerating  the  amoeboid  movements  of  the  pale 
corpuscles.  Sketch  one  at  intervals  of  a  minute  (a)  in  the  cold,  (6)  whilst 
warmed. 


FIG.  19. — WHITE  COEPUSCLES  OF  FROG'S  BLOOD  MIGRATED  FROM  SHRUNKEN 
CLOT  WITHIN  A  CAPILLARY  TUBE.  (From  Sanderson's  Handbook  for  the 
Physiological  Laboratory.) 

3.  Take  some  yeast  which  has  been  mixed  with  salt  solution,  and  mix  a 
little  of  the  yeast  and  salt  solution  with  a  fresh  drop  of  newt's  blood,  slightly 
oiling  the  edge  of  the  cover-glass  as  before.  Endeavour  to  observe  the  incep- 
tion of  torulse  by  the  white  corpuscles.  Sketch  one  or  two  corpuscles  con- 
taining torulse. 

Milk-globules  or  particles  of  carbon  or  of  vermilion  may  also  be  used  for 
this  experiment,  but  the  process  of  inception  is  most  readily  observed  with 
the  yeast  particles. 

1  For  exact  work,  an  apparatus  somewhat  more  complex  than  the  above  is  required. 
For  description  of  such  see  A  Course  of  Practical  Histology. 


22  THE  ESSENTIALS  OF  HISTOLOGY. 

4.  At  the  beginning  of  the  lesson  collect  a  drop  of  newt's  blood  into  a  fine 
capillary  tube,  seal  the  ends  of  the  tube,  and  mount  in  it  a  drop  of  oil  of 
cedar  or  Canada  balsam.     Towards  the  end  of  the  lesson  examine  it  again  to 
see  white  corpuscles  emigrating  from  the  shrunken  clot  (see  fig.  19). 

5.  To  obtain  a  specimen  showing  white  corpuscles  in  amoeboid  condition, 
make  a  preparation  of  newt's  blood,  mixed  with  salt  solution,  and  set  it  aside 
for  ten  minutes.     By  this  time  the  corpuscles  will  be  freely  amoeboid,  and 
will  probably  show  well-marked  pseudopodia.     To  fix  them  in  this  condition 
let  a  jet  of  steam  from  the  spout  of  a  kettle  play  for  two  or  three  seconds 
upon  the  cover-glass.     The  heat  instantaneously  kills  the  corpuscles,  and 
they  are  fixed  in  the  form  they  presented  at  the  moment  the  steam  was 
applied.     They  may  now  be  stained  by  passing  dilute  hsematoxylin  solution 
under  the  cover-glass,  and  this  may  be  replaced  by  dilute  glycerine,  after 
which  the  cover  may  be  cemented  and  the  preparation  kept. 

The  amoeboid  phenomena  which  are  exhibited  by  the  protoplasm  of 
the  colourless  blood-corpuscles  consist,  in  the  first  place,  of  spontaneous 
changes  of  form,  produced  by  the  throwing  out  of  processes  or  pseudo- 
podia  in  various  directions.  When  first  thrown  out  the  pseudopodia  are 
composed  of  hyaloplasm  alone,  and  they  are  probably  produced  by  a 
flowing  of  the  hyaloplasm  from  out  the  meshes  of  the  protoplasm 
(see  p.  2).  If  the  corpuscle  is  stimulated,  either  mechanically,  as  by 
tapping  the  cover-glass,  or  electrically,  the  hyaloplasm  is  withdrawn 
again  into  the  spongioplasm,  and  the  pseudopodia  are  thereby  retracted^ 
the  corpuscle  becoming  spherical.  A  change  of  form,  caused  by  the 
protrusion  of  the  pseudopodia,  may,  when  active,  be  followed  by  changes 
in  place  or  actual  locomotion  (migration)  of  the  corpuscle.  When  a 
pseudopodiuin,  or  the  external  surface  of  the  corpuscle,  comes  in  contact 
with  any  foreign  particle,  the  hyaloplasm  tends  to  flow  round  and 
enwrap  the  particle,  and  particles  thus  incepted  may  then  be  conveyed 
by  the  corpuscle  in  its  locomotory  changes  from  one  place  to  another. 
This  property  appears  to  play  an  important  part  in  many  physiological 
and  pathological  processes. 

It  is  probable  that  particles  of  organic  matter  which  are  taken  up  by 
the  pale  corpuscles  may  undergo  some  slow  process  of  intracellular 
digestion  within  their  protoplasm. 

The  processes  of  the  granular  corpuscles  are  generally  quite  clear  at 
first,  and  the  granules  afterwards  flow  into  them. 

The  migration  of  the  colourless  corpuscles  from  the  blood-vessels  into 
the  surrounding  tissue,  or  from  a  blood-clot  into  the  surrounding  serum 
(fig.  19),  is  owing  to  these  amoeboid  properties. 

The  conditions  which  are  most  favourable  to  this  amoeboid  activity  of 
the  white  corpuscles  are  (1)  the  natural  slightly  alkaline  medium,  such 
as  plasma,  serum,  or  lymph,  or  faintly  alkaline  normal  saline  solution. 
Any  increase  of  density  of  the  medium  produces  a  diminution  of 


AMCEBOID  PHENOMENA. 


23 


amoeboid  activity,  whilst,  on  the  other  hand,  a  slight  decrease  in  its 
density  has  the  opposite  effect  j  (2)  a  certain  temperature.  In  warm- 
blooded animals  the  phenomena  cease  below  about  10°C.  When 
gradually  warmed  they  become  more  and  more  active  up  to  a  certain 
point,  the  maximum  being  a  few  degrees  above  the  natural  temperature 
of  the  blood.  Above  this  point  they  become  spheroidal  and  at  a 


FIG.  20.— CHANGES  OF  FORM  OF  A  WHITE  CORPUSCLE  OF  NEWT'S  BLOOD,  SKETCHED  AT 
INTERVALS  OF  A  FEW  MINUTES,  SHOWING  THE  INCEPTION  OF  TWO  SMALL  GRANULES 
AND  THE  CHANGES  OF  POSITION  THESE  UNDERWENT  WITHIN  THE  CORPUSCLE. 


FIG.  21. — THREE  AMCEBOID  WHITE  CORPUSCLES  OF  THE  NEWT,  KILLED  BY 
INSTANTANEOUS  APPLICATION  OF  STEAM. 

a,  a  coarsely  granular  cell ;  b,  c,  ordinary  cells.  The  nuclei  appear  multiple, 
but  are  seen  to  be  connected  by  fine  filaments  of  chromoplasm  traversing 
the  protoplasm. 

somewhat  higher  temperature  their  protoplasm  is  coagulated  and  killed. 
Acids  at  once  kill  the  corpuscles  and  stop  the  movements.  Narcotic 
gases  and  vapours,  such  as  carbonic  acid  gas  or  chloroform  vapour,  also 
arrest  the  movement,  but  it  recommences  after  a  time  if  their  action  is 
discontinued. 


24  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON    VI. 

EPITHELIUM. 

1.  MOUNT  a  drop  of  saliva  and  examine  first  with  a  low,  afterwards  with  a 
high  power.  Observe  the  nucleated  epithelium-cells,  some  single,  and  others 
still  adhering  together  by  overlapping  edges.  Measure  three  or  four,  and  also 
their  nuclei.  Sketch  one  or  two  on  the  flat  and  one  edgeways.  Notice  the 
salivary  corpuscles,  which  are  like  white  blood-corpuscles  swollen  out  by 
imbibition  of  water. 

2.  Put  a  small  shred  of  human  epidermis  into  a  drop  of  strong  caustic  potash 
solution  for  five  minutes.     Then  break  it  up  in  water  with  needles,  cover 
and  examine.     Observe  the  now  isolated  swollen  cells.     M  easure  some. 

3.  Study  the  arrangement  of  the  cells  in  a  section  through  some  stratified 
epithelium,  such  as  that  of  the  mouth,  skin,  or  cornea.1    Notice  the  changes 
in  shape  of  the  cells  as  they  are  traced  towards  the  free  surface.     Measure 
the  thickness  of  the  epithelium.     Count  the  number  of  layers  of  cells. 

4.  Study  the  minute  structure  of  epithelium-cells  and  their  nuclei,  both 
at  rest  and  dividing,  in  sections  of  the  skin  of  the  newt's  tail  or  in  shreds  of 
epidermis  of  the  salamander-tadpole.    The  preparation  may,  for  this  purpose, 
be   stained   either  with   hsematoxylin   or  with   some   aniline   dye   such   as 
safranin.2 

Sketch  an  epithelium -cell  with  resting  nucleus,  and  others  with  nuclei  in 
different  phases  of  karyokinesis. 

An  epithelium  is  a  tissue  composed  entirely  of  cells  separated  by  a 
very  small  amount  of  intercellular  substance  (cement-substance),  and 
generally  arranged  so  as  to  form  a  membrane  covering  either  an 
external  or  an  internal  free  surface. 

The  structure  of  epithelium-cells,  and  the  changes  which  they 
undergo  in  cell-division,  are  best  seen  in  the  epidermis  of  the  newt 
or  of  the  salamander-tadpole;  in  the  latter  especially  the  cells  and 
nuclei  are  much  larger  than  in  mammals. 

Structure  of  the  cells.— Each  epithelium-cell  consists  of  protoplasm 
containing  a  nucleus.  The  protoplasm  may  either  look  granular,  or  it 
may  have  a  reticulated  appearance.  In  some  kinds  of  epithelium  it  is 
striated.  The  nucleus  is  a  round  or  oval  vesicle  lying  in  the  proto- 
plasm. Usually  there  is  only  one,  but  there  may  be  two  or  more. 

1  The  methods  of  preparing  sections  are  given  in  the  Appendix. 

2  The  methods  which  serve  the   purpose  of   exhibiting  the  division  of  nuclei  are 
given  in  the  Appendix. 


EPITHELIUM. 


25 


The  cell-substance  is  often  modified  in  its  chemical  nature  ;  its  external 
layer  may  become  hardened  to  form  a  sort  of  menfbrane,  or  the  whole 
cell  may  become  horny  (keratinised) ;  or  the  cell  may  develop  fibrils 
within  it,  and  passing  from  it  into  adjacent  cells,  or  lastly,  there  may 
be  an  accumulation  of  materials  within  the  cell  which  are  ultimately 
either  used  by  the  organism,  as  in  the  ordinary  secreting  glands,  or 
eliminated  as  waste  products  as  in  the  kidney. 


FIG.  22.— EPITHELIUM-CELLS  OF  SALAMANDEK  LARVA  IN  DIFFERENT  PHASES  OF. 
DIVISION  BY  KARYOKINESIS.     (Flemming.) 

Division  of  the  cells. — The  division  of  a  cell  is  preceded  by  the 
division  of  its  attraction-sphere,  and  this  again  appears  to  determine 
the  division  of  the  nucleus.  The  latter,  in  dividing,  passes  through  a 
series  of  remarkable  changes  (fig.  22),  which  may  thus  be  briefly 
summarised : — 

1.  The  network  of  chromoplasm-filaments   of   the   resting   nucleus 


26 


THE  ESSENTIALS  OF  HISTOLOGY. 


becomes  transformed  into  a  sort  of  skein,  formed  apparently  of  one 
long  convoluted  nTament ;  the  nuclear  membrane  and  the  nucleoli  dis- 
appear or  are  merged  into  the  skein  (fig.  22,  b,  c,  d).  Sometimes  the 
skein  becomes  looped  in  and  out  of  a  central  space ;  this  form  is  termed 
the  rosette  (e). 


FlG.  23.— A  DIVIDING  CELL,  SHOWING  ATTRACTION  PARTICLE  AT  EITHER  POLE  OF  NUCLEUS 
FROM  WHICH  THE  GRANULES  OF  THE  PROTOPLASM  ARE  SEEN  RADIATING,  AND  WITH 
WHICH  ALSO  THE  SPINDLE-SHAPED  SYSTEM  OF  ACHROMATIC  FIBRES  TRAVERSING  THE 
NUCLEUS  IS  CONNECTED.  THE  CHROMOSOMES,  SIX  IN  NUMBER,  JARE  ARRANGED 
ASTRALLY  AT  THE  EQUATOR  OF  THE  SPINDLE.  (Rabl.) 

of 


orruxHc\ 
spindle-      I 
wttk-centraL  [ 
/xx>rttek\ 


FIG.  24.— A  NUCLEUS  AT  A  STAGE  SIMILAR  TO  THAT  SHOWN  IN  THE  LAST  FIGURE,  BUP 

SEEN  FROM  ONE  OF  THE  POLES  INSTEAD  OF  IN  PROFILE.    THE  SPINDLE  IS  REPRESENTED 
FORESHORTENED.      EIGHT  CHROMOSOMES  ARE  REPRESENTED.      (Rabl.) 

2.  The  filament  breaks  into  a  number  of  separate  portions,  often 
V-shaped,  and  termed  chromosomes.    The  number  of  chromosomes  varies 
with  the  species  of  animal ;  in  some  animals  the  dividing  nuclei  may 
contain  at  this  stage  only  four  chromosomes,  in  others  24  or  more. 
As  soon  as  they  become  distinct  they  are  usually  arranged  radially  like 
a  star  (aster,  /,  g). 

3.  Each  of  the  chromosomes  splits  longitudinally  into  two,  so  that 
they  are  now  twice  as  numerous  as  before  (stage  of  cleavage,  g,  h). 

4.  The  fibres  separate  into  two  groups,  the  ends  being  for  a  time 
interlocked  (stage  of  metakmesis,  i,  j,  k). 

5.  The  two  groups  pass  to  the  opposite  poles  of  the  now  elongated 
nucleus  and  form  a  star-shaped  figure  (/)  at  each  pole  (dyaster).     Each 
of  the  stars  represents  a  daughter-nucleus. 

6.  7,  8.  Each  star  of  the  dyaster  goes  through  the  same  changes  as 


EPITHELIUM.  27 

the  original  nucleus,  but  in  the  reverse  order — viz.,  skein  at  first  more 
open  and  rosette-like  (m),  then  closer  (n),  then  a  network  (o,  p,  q);  passing 
finally  into  the  typical  reticular  condition  of  a  resting  nucleus. 

The  protoplasm  of  the  cell  divides  soon  after  the  formation  of  the 
dyaster  (m).  During  division  fine  lines  are  seen  in  the  protoplasm, 
radiating  from  the  ends  of  the  nucleus.  Other  lines  produced  by  a 
spindle-shaped  system  of  achromatic  fibres  lie  within  the  nucleus,  diverg- 
ing from  the  poles  towards  the  equator  (figs.  23, 24);  they  are  far  less  easily 
seen  than  the  other  or  chromatic  fibres,  but  are  not  less  important,  for 
they  are  derived  from  the  attraction-spheres,  which,  as  we  have  seen, 
always  initiate  the  division  of  a  cell.  Moreover,  the  achromatic  fibres 
within  the  nucleus  appear  to  form  guides  along  which  the  chromosomes 
or  chromoplasmic  filaments  are  conducted  towards  its  poles. 

Classification  of  epithelia. — Epithelia  are  classified  according  to  the 
shape  and  arrangement  of  the  component  cells.  Thus  we  speak  of 
scaly  or  pavement,  cubical,  columnar,  polyhedral,  and  spheroidal  epithelium. 
All  these  are  simple  epithelia,  with  the  cells  only  one  layer  deep.  If 
forming  several  superposed  layers,  the  epithelium  is  said  to  be  stratified, 
and  then  the  shape  of  the  cells  differs  in  the  different  layers.  Where 
there  are  only  three  or  four  layers  in  a  stratified  epithelium,  it  is 
termed  transitional. 

Stratified  epithelium  covers  the  anterior  surface  of  the  cornea, 
lines  the  mouth,  pharynx  (lower  part),  and  gullet,  and  forms  the  epi- 


FIG.  25. — SECTION  OF  THE  STRATIFIED  EPITHELIUM  COVERING  THE  FRONT  OF 
THE  CORNEA  OF  THE  EYE. 

c,  lowermost  columnar  cells ;  p,  polygonal  cells  above  these  ;  fl,  flattened  cells  near  the  surface. 
Between  the  cells  are  seen  intercellular  channels  bridged  over  by  processes  which  pass 
from  cell  to  cell. 

dermis  which  covers  the  skin.  In  the  female  it  lines  the  vagina  and 
part  of  the  uterus.  The  cells  nearest  the  surface  are  always  flattened 
and  scale-like  (fig.  25,  fl\  fig.  26),  whereas  the  deeper  cells  are  more 
rounded  or  polyhedral,  and  those  of  the  deepest  layer  generally  some- 
what columnar  in  shape  (fig.  25,  c).  Moreover,  the  deeper  cells  are  soft 
and  protoplasmic,  and  are  separated  from  one  another  by  a  system  of 


THE  ESSENTIALS  OF  HISTOLOGY. 


intercellular  channels,  which  are  bridged  across  by  numerous  fibres 
passing  from  cell  to  cell,  and  giving  the  cells,  when  separated,  the 
appearance  of  being  beset  with  short  spines  (prickle-cells  of  Max 
Schultze). 

The  deeper  cells  multiply  by  division,  the  nuclei  first  dividing  in  the 
manner  just  described.  The  newly  formed  cells  tend  as  they  enlarge  to 
push  those  external  to  them  nearer  to  the  surface,  from  which  they  are 
eventually  thrown  off.  As  they  approach  the  surface  they  become  hard 
and  horny,  and  in  the  case  of  the  epidermis  lose  entirely  their  cellular 
appearance,  which  can,  however,  be  in  a  measure  restored  by  the  action 
of  potash  (§  2).  The  cast-off  superficial  cells  of  the  stratified  epithelium 
of  the  mouth,  which  are  seen  in  abundance  in  the  saliva  (§  1),  are  less 
altered,  and  the  remains  of  a  nucleus  is  still  visible  in  them  (fig.  26). 

Simple  scaly  or  pavement  epithelium 
is  found  in  the  saccules  of  the  lungs,  in 
those  of  the  mammary  gland  when  in- 
active,  in  the  kidney  (in  the  tubes  of 
ft«t**'j/A  x  ""'""'   °a<"V     ^Y      Henle),  and  also  lining  the  cavities  of 
jv/^-^^^^'          serous   membranes    (fig.    27),    and    the 

^-^^  heart,    blood-vessels,     and     lymphatics. 

FIG.  2(3.—  EPITHELIUM-SCALES  FKOM  ___.  .  .  • 

THE  INSIDE  OF  THE  MOUTH.    (Mag-  When   occurring    on    internal    surfaces, 
nified  200  diameters.)  such  as  those  of  the  serous  membranes, 

blood-vessels,  and  lymphatics,  it  is  often  spoken  of  as  endothelium. 


FIG.  27.— PAVEMENT  EPITHELIUM  OR  ENDOTHELIUM  OF  A  SEROUS 
MEMBRANE.     NITRATE  OF  SILVER  PREPARATION. 


POLYHEDEAL  OR  SPHEROIDAL  EPITHELIUM.  29 

Polyhedral  or  spheroidal  epithelium  is  characteristic  of  many  secret- 
ing glands.  Columnar  and  ciliated  epithelium  are  for  the  most  part 
found  covering  the  inner  surface  of  mucous  membranes ;  which  are 
membranes  moistened  by  mucus  and  lining  passages  in  communication 
with  the  exterior,  such  as  the  alimentary  canal  and  the  respiratory  and 
generative  passages. 

The  detailed  study  of  most  of  these  may  be  reserved  until  the 
organs  in  which  they  occur  are  respectively  dealt  with. 

The  hairs  and  nails  and  the  enamel  of  the  teeth  are  modified  epithelial 
tissues. 


30  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON    VII. 

COLUMNAR  AND  CILIATED  EPITHELIUM,  AND 
TRANSITIONAL  EPITHELIUM. 

1.  TAKE  a  piece  of  rabbit's  intestine  which  has  been  two  days  in  chromic 
acid  solution  (1  part  chromic  acid  to  2,000  normal  saline  solution).  Scrape  the 
inner  surface  with  a  scalpel,  break  up  the  scrapings  in  a  drop  of  water  on  a 
slide.  Add  a  small  piece  of  hair  to  avoid  crushing,  and  cover  the  preparation. 
The  tissue  may  then  be  still  further  broken  up  by  tapping  the  cover-glass. 
Sketch  one  or  two  columnar  cells  and  also  a  row  of  cells.  Measure  two  or 
three  cells  and  their  nuclei. 

To  keep  this  preparation,  place  a  drop  of  very  dilute  hsematoxylin  solution 
at  one  edge  of  the  cover-glass.  When  the  hsematoxylin  has  passed  in  and 
has  stained  the  cell-nuclei,  place  a  drop  of  glycerine  at  the  same  edge  and 
allow  it  slowly  to  diffuse  under  the  cover-glass.  Cement  this  another  day. 
Osmic  acid  (1  per  cent.)  may  be  used  in  place  of  hsematoxylin. 

2.  Break  up  in  glycerine  a  shred  of  epithelium  from  a  piece  of  frog's 
intestine  that  has  been  treated   with   osmic   acid,  and   has  subsequently 
macerated  in  water  for  a  few  days.     The  cells  easily  separate  on  tapping  the 
cover-glass.    They  are  larger  than  those  of  the  rabbit  and  exhibit  certain 
points  of  structure  better.     Measure  and  sketch  one  or  two  cells. 

The  cover-glass  may  be  at  once  fixed  by  gold  size. 

3.  Prepare  the  ciliated  epithelium  from  a  trachea  that  has  been  in  chromic 
acid  solution  (1  to  2,000  normal  saline)  for  two  days,  in  the  same  way  as  in 
§  1.     Measure  in  one  or  two  of  the  cells  (a)  the  length  of  the  cells,  (6)  the 
length  of  the  cilia,  (c)  the  size  of  the  nucleus.     Sketch  two  or  three  cells. 

This  preparation  is  to  be  stained  and  preserved  as  in  §  1. 

4.  Make  a  similar  teased  preparation  of  the  epithelium   of  the  urinary 
bladder,  which  is  to  be  distended  with  bichromate  of  potash  solution  (1  part  to 
800  of  water),  and  after  an  hour  or  two  cut  open  and  placed  in  more  of  the 
same  solution.      Observe  the  large  flat  superficial  cells,  and  the  pear-shaped 
cells  of  the  second  layer.    Measure  and  sketch  one  or  two  of  each  kind.    The 
cells  will  vary  greatly  in  appearance  according  to  the  amount  of  distension' 
of  the  organ. 

Stain  and  preserve  as  in  §§  1  and  3. 

All  the  above  varieties  of  epithelium  will  afterwards  be  studied  in  situ 
when  the  organs  where  they  occur  come  under  consideration. 


Columnar  epithelium. — The  cells  of  a  columnar  epithelium  (fig.  28) 
are  prismatic  columns,  which  are  set  closely  side  by  side,  so  that  when 
seen  from  the  surface  a  mosaic  appearance  is  produced.  They  often 
taper  somewhat  towards  their  attached  end,  which  is  generally  trun- 
cated, and  set  upon  a  basement  membrane.  Their  free  surface  is 
covered  by  a  thick  striated  border  (fig.  29,  str),  which  may  sometimes 


COLUMNAE  EPITHELIUM.  31 

become  detached  in  teased  preparations.  The  protoplasm  of  the  cell  is 
highly  vacuolated  and  reticular,  and  fine  longitudinal  striae  may  be  seen 
in  it,  which  appear  continuous  with  the  striae  of  the  free  border.  The 
nucleus  (n)  is  oval  and  reticular.  The  lateral  borders  of  the  cells  are 
often  somewhat  irregular  or  jagged,  the  result  of  the  pressure^  of^ 
amoeboid  lymph-cells,  which  are  generally  found  between  the  columnar 
cells,  at  least  in  the  intestine.  After  a  meal  containing  fat  the  cells  may 
contain  fat-globules,  which  become  stained  black  in  the  osmic  pre- 
paration. 


FIG.  28. — A  ROW  OF  COLUMNAR  CELLS  FROM  THE  INTESTINE  OF  THE  RABBIT. 
Smaller  cells  are  seen  between  the  epithelium-cells  ;  these  are  lymph-corpuscles. 

Columnar  epithelium-cells  are  found  lining  the  whole  of  the  interior 
of  the  stomach  and  intestines :  they  are  also  present  in  the  ducts  of 
most  glands,  and  sometimes  also  in  their  secreting  tubes  and  saccules. 
The  epithelium  which  covers  the  ovary  also  has  a  modified  columnar 
shape,  but  cells  having  all  the  structural  peculiarities  indicated  above 
are  found  only  in  the  alimentary  canal  and  in  its  diverticula. 


I. 

FIG.  29. — COLUMNAR  EPITHELIUM-CELLS  OF  THE  RABBIT'S  INTESTINE. 

The  cells  have  been  isolated  after  maceration  in  very  weak  chromic  acid.  The  cells  are  much 
vacuolated,  and  one  of  them  has  a  fat-globule  near  its  attached  end  ;  the  striated  border 
(str)  is  well  seen,  and  the  bright  disk  separating  it  from  the  cell-protoplasm  ;  n,  nucleus 
with  intranuclear  network  ;  a,  a  thinned-out  wing-like  projection  of  the  cell  which  prob- 
ably fitted  between  two  adjacent  cells. 

Goblet-cells. — Some  columnar  cells,  and  also  cells  of  glandular, 
ciliated  and  transitional  epithelia,  contain  mucigen,  which  is  laid  down 
within  the  cell  in  the  form  of  granules  (fig.  33,  m\  m2)  and  may 
greatly  distend  the  part  of  the  cell  nearest  the  free  border.  When  the 
mucigen  is  extruded  as  mucus,  this  border  is  thrown  off,  and  the  cell 
takes  the  form  of  an  open  cup  or  chalice  (fig.  30  and  fig.  33,  m3). 


32 


THE  ESSENTIALS  OF  HISTOLOGY. 


Ciliated  epithelium. — The  cells  of  a  ciliated  epithelium  are  also 
usually  columnar  in  shape  (fig.  31),  but  in  place  of  the  striated  border 
the  cell  is  surmounted  by  a  bunch  of  fine  tapering  filaments  which, 
during  life,  move  spontaneously  to  and  fro,  and  serve  to  produce  a 
current  of  fluid  over  the  surface  which  they  cover. 

The  cilia  are  to  be  regarded  as  active  prolongations  of  the  cell- 
protoplasm.  The  border  upon  which  they  are  set  is  bright,  and 
appears  formed  of  little  juxtaposed  knobs,  to  each  of  which  a  cilium  is 
attached.  In  the  large  ciliated  cells  which  line  the  alimentary  canal 
of  some  molluscs  (fig.  32),  the  knob  may  be  observed  to  be  prolonged 
into  the  protoplasm  of  the  cell  as  a  fine  varicose  filament,  termed  the 
rootlet  of  the  cilium.  These  filaments  perhaps  represent  the  longi- 


FIG.  30.— GOBLET-CELL 
FROM  THE  TRACHEA. 
(Klein.) 


FIG.  31. — COLUMNAR  CILI- 
ATED EPITHELIUM-CELLS 
FROM  THE  LOWER  PART 

OF  THE  NASAL  PASSAGES. 
EXAMINED  FRESH  IN 
SERUM.  (Sharpey.) 


FIG.  32. — CILIATED  CELL, 
FROM    THE   INTESTINE 

OF  A  MOLLUSC.    (Engel- 

mann.) 


tudinal  striae  often  seen  in  the  protoplasm  of  the  columnar  cell,  the 
bunch  of  cilia  being  homologous  with  the  striated  border.  The  proto- 
plasm and  nucleus  have  a  similar  vacuolated  and  reticular  structure  in 
both  kinds  of  cell. 


CILIATED  EPITHELIUM. 


Ciliated  epithelium  is  found  throughout  the  whole  extent  of  the 
air-passages  and  their  prolongations  (but  not  in  the  part  of  the  nostrils 
supplied  by  the  olfactory  nerves,  nor  in 
the  lower  part  of  the  pharynx);  in  the 
Fallopian  tubes  and  the  greater  part  of 
the  uterus ;  in  some  of  the  efferent  ducts 
of  the  testicle  (where  the  cilia  are  longer 
than  elsewhere  in  the  body);  in  the  ven- 
tricles of  the  brain,  and  the  central  canal 
of  the  spinal  cord;  and,  according  to 
some  authorities,  in  the  convoluted  tubules 
of  the  kidney. 

Transitional  epithelium  is  a  stratified 
epithelium  consisting  of  only  two  or 
three  layers  of  cells.  It  occurs  in  the 
urinary  bladder,  the  ureter,  and  the 
pelvis  of  the  kidney.  The  superficial 
cells  (fig.  34,  a)  are  large  and  flattened; 
they  often  have  two  nuclei.  On  their 
under  surface  they  exhibit  depressions, 
into  which  fit  the  larger  ends  of 
pyriform  cells,  which  form  the  next  layer  (fig.  34,  b).  Between  the 
tapered  ends  of  the  pyriform  cells  one  or  two  layers  of  smaller  poly- 


FIG.  33.— CILIATED  COLUMNAR 
EPITHELIUM,  FROM  THE  TRACHEA 
OF  A  RABBIT. 

wii,  m2,  ?)i3,  mucus-secreting  cells  in 
various  stages  of  mucigen  formation. 
The  preparation  was  treated  with 
dilute  chromic  acid  in  the  manner 
recommended  in  the  instructions 
for  practical  work. 


FIG.  34.— EPITHELIAL  CELLS  FROM  THE  BLADDER  OF  THE  RABBIT.    (Klein.) 
(Magnified  500  diameters.) 

a,  large  flattened  cell  from  the  superficial  layer,  with  two  nuclei  and  with  strongly  marked 
ridges  and  intervening  depressions  on  its  under  surface  ;  6,  pear-shaped  cell  of  the  second 
layer  adapted  to  a  depression  on  one  of  the  superficial  cells. 


hedral  cells  are  found, 
deeper  cells. 


The  epithelium  is  renewed  by  division  of  these 


34 


THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  VIII. 


STUDY  OF  CILIA  IN  ACTION. 


1.  MOUNT  in  sea- water  one  or  two  bars  of  the  gill  of  the  marine  mussel 
(fig.  35).  Study  the  action  of  the  large  cilia.  Now  place  the  preparation 
upon  the  copper  warm  stage  (see  Lesson  Y.)  and  observe  the  effect  of  raising 
the  temperature. 


FIG.  35.— YALVE  OF  MUSSEL  (MYTILUS  EDULIS)  SHOWING  br,  br,  THE  EXPANDED 

G  ILLS   OR   BRANCHIAE,    WHICH,    OWING   TO    THE    LITTLE  BARS    OF    WHICH    THEY 
AR»  COMPOSED,    PRESENT  A  STRIATED  ASPECT. 

ml,  mantle ;  m,  cut  adductor  muscle  ;  it  mass  of  viscera  ;  the  dark  projection  just  above  is  the  foot. 

Keep  this  preparation  until  the  end  of  the  lesson,  by  which  time  many  of 
the  cilia  will  have  become  languid.  When  this  is  the  case  pass  a  drop  of 
dilute  potash  solution  (1  part  KHO  to  1,000  of  sea- water)  under  the  cover-glass 
and  observe  the  effect. 


FIG.  36. — MOIST  CHAMBER  ADAPTED  FOR  PASSING  A  GAS  OR  VAPOUR  TO  A 
PREPARATION  UNDER  THE  MICROSCOPE. 

2.  Cement  with  sealing-wax  a  piece  of  small  glass  tubing  to  a  slide  so  that 
one  end  of  the  tube  conies  nearly  to  the  centre  of  the  slide.     To  do  this 


STUDY  OF  CILIA  IN  ACTION. 


35 


effectually  the  slide  must  be  heated  and  some  sealing-wax  melted  on  to  it 
and  allowed  to  cool.  The  glass  tube  is  then  made  hot  and  applied  to  the 
slide,  embedding  itself  as  it  does  so  in  the  sealing-wax.  On  this  put  a  ring 
of  putty  or  modelling  wax  (half  an  inch  in  diameter  and  rising  above  the 
glass  tube)  so  as  to  include  the  end  of  the  tube.  Make  a  deep  notch  in  the 
ring  opposite  the  tube.  Place  a  small  drop  of  water  within  the  ring  (fig.  36). 

Put  a  bar  from  the  gill  upon  a  cover-glass  in  the  least  possible  quantity  of 
sea- water  ;  invert  the  cover-glass  over  the  putty  ring,  and  press  it  gently 
down.  The  preparation  hangs  in  a  moist  chamber  within  which  it  can  be 
studied  through  the  cover-glass,  and  into  which  gases  or  vapours  can  be  passed 
and  their  effects  observed. 

Pass  CO-2  through  the  chamber,  and  after  observing  the  effect  replace  it  by 
air  (see  fig.  37).  Repeat  with  chloroform  vapour  instead  of  CO;). 


The  movement  of  cilia. — When  in  motion  a  cilium  is  bent  quickly 
over  in  one  direction  with  a  lashing  whip-like  movement,  immediately 
recovering  itself.  When  vigorous  the  action  is  so  rapid,  and  the 
rhythm  so  frequent  (ten  or  more  times  in  a  second)  that  it  is  impossible 
to  follow  the  motion  with  the  eye.  All  the  cilia  upon  a  ciliated  surface 
are  not  in  action  at  the  same  instant,  but  the  movement  travels  in 


FIG.  37.— METHOD  OF  SUBJECTING  A  PREPARATION  TO  A  STREAM  OF  CARBONIC 

ANHYDRIDE. 

b,  bottle  containing  marble  and  hydrochloric  acid  ;  &',  wash-bottle,  connected  by  indiarubber 
tube,  t,  with  the  moist  chamber,  s. 

waves  over  the  surface.  If  a  cell  is  detached  from  the  general  surface, 
its  cilia  continue  to  act  for  a  while,  but  at  once  cease  if  they  are 
detached  from  the  cell. 

The  rhythm  is  slowed  by  cold,  quickened  by  warmth,  but  heat 
beyond  a  certain  point  kills  the  cells.  The  movement  will  continue 
for  some  time  in  water  deprived  of  oxygen.  Both  C02  gas  and  chloro- 
form vapour  arrest  the  action,  but  it  recommences  on  restoring  air. 


36  THE  ESSENTIALS  OF  HISTOLOGY. 

Dilute  alkaline  solutions  quicken  the  activity  of  cilia,  or  may  even 
restore  it  shortly  after  it  has  ceased. 

Various  attempts  have  been  made  to  explain  the  manner  in  which 
cilia  act,  some  supposing  that  they  are  themselves  contractile,  others 
that  their  movement  is  a  passive  one,  and  that  the  real  movement  is  at 
their  rootlets  in  the  protoplasm  of  the  cell.  The  bending-over  action 
can  also  be  supposed  to  be  due  to  the  alternate  flowing  and  ebbing 
of  hyaloplasm  from  the  body  of  the  cell  into  hollow  permanent  cell- 
processes,  i.e.  the  cilia ;  if  we  assume  that  one  side  of  each  cilium  is 
less  extensible  than  the  other,  it  must  necessarily  be  bent  over  in  the 
manner  usually  observed.  Some  cilia,  however,  have  a  spiral  action 
rather  than  the  simple  to  and  fro  movement;  in  this  case  we  may 
assume  that  the  line  of  less  extensibility  passes  not  straight  along  one 
side  of  the  cilium,  but  spirally  round  it. 

This  hypothesis  has  the  advantage  that  it  permits  ciliary  motion  to 
be  brought  into  the  same  category  as  amoeboid  movements,  in  so  far 
that  both  are  explicable  by  the  flowing  of  hyaloplasm  out  of  and  into 
the  reticulum  of  spongioplasm. 


THE  CONNECTIVE  TISSUES.  37 


LESSON  IX. 
THE  CONNECTIVE  TISSUES. 

AEEOLAR  AND   ADIPOSE   TISSUE,    RETIFORM   TISSUE. 

I.  TAKE  a  little  of  the  subcutaneous  tissue  or  of  the  intermuscular  connective 
tissue  of  a  rabbit  or  guinea-pig  and  spread  it  out  with  needles  on  a  dry  slide 
into  a  large  thin  film.  Keep  the  centre  moist  by  occasionally  breathing  on 
it,  but  allow  the  edges  to  dry  to  the  slide.  Before  commencing  put  a  drop 
of  salt  solution  on  a  cover-glass,  and  now  invert  this  over  the  film.  Ex- 
amine with  a  high  power.  Sketch  one  or  two  bundles  of  white  fibres  arid 
also  one  or  two  elastic  fibres,  distinguishable  from  the  former  by  their 
sharp  outline,  isolated  course,  and  by  their  branching.  Sketch  also  one  or 
more  connective-tissue  corpuscles,  if  any  such  are  visible  in  the  clear  inter- 
spaces. Look  also  for  migratory  cells  (lymph-corpuscles).  Next  carefully 
remove  the  cover-glass  and  replace  the  salt  solution  by  dilute  acetic  acid 
(1  per  cent.).  Watch  its  effect  in  swelling  the  white  fibres  and  bringing 
more  clearly  into  view  the  elastic  fibres  and  corpuscles.  Look  for  constricted 
bundles  of  white  fibres. 

2.  Make  another  film  in  the  same  way,  but  mount  in  dilute  magenta 
solution 1  instead  of  saline  solution.     The  elastic  fibres  are  deeply  stained  by 
the  dye  ;   the  cells  are  also  well  shown.     Cement  the  cover-glass  at  once 
with  gold  size. 

3.  Prepare  another  film  of   the   subcutaneous  tissue,  including  a  little 
adipose  tissue.     Mount,  as  before,  in  dilute  magenta  solution,  with  a  piece 
of  hair  under  the  cover-glass  to  keep  this  from  pressing  unduly  upon  the 
fat-cells.     Cement  at  once  with  gold  size.     Examine  first  with  a  low  and 
afterwards  with  a  high  power.     The  nucleus  and  envelope  of  the  fat-cell 
are  well  brought  out  by  the  magenta,  and  if  from  a  young  animal,  fat-cells 
will  be  found  in  process  of  formation.     Measure  and  sketch  two  or  three 
of  the  cells. 

4.  Spread  out  another  large  film  of  connective  tissue,  letting  its  edges  dry 
to  the  slide,  but  keeping  the  centre  moist  by  the  breath.     Place  on  its  centre 
a  large  drop  of  nitrate  of  silver  solution  (1  per  cent.).     After  ten  minutes 
wash  this  away  with  distilled  water,  and  expose  to  direct  sunlight  until 
stained  brown.     Then  dehydrate  with  alcohol,  replace  the  alcohol  by  clove- 
oil,  and  this  by  Canada  balsam  dissolved  in  xylol.     Cover2  and  examine. 
Sketch  the  outlines  of  two  or  three  of  the  cell-spaces. 

5.  Mount  in  dilute  glycerine  and  water,  coloured  by  magenta,  a  section  of 
lymphatic  gland  which  has  been  immersed  for  a  few  minutes  in  0'5  per  cent, 
solution  of  caustic  potash.     The  alkali  destroys  the  cells,  and  thus  allows 
the  network  of  fibres  which  compose  the  retiform  tissue  to  be  seen.     They 
are  in  all  respects  like  the  fibrils  of  areolar  tissue. 

1  See  Appendix. 

2  Preparations  which  are  mounted  in  Canada  balsam  solution  will  soon  become  fixed 
by  the  hardening  of  the  Canada  balsam  at  the  edges  of  the  cover-glass.     They  must  on 
no  account  be  cemented  with  gold  size. 


38 


THE  ESSENTIALS  OF  HISTOLOGY. 


The  connective  tissues  include  areohir  tissue,  adipose  tissue,  elastic 
tissue,  fibrous  tissue,  retiform  and  lymplwid  tissue,  cartilage  and  lone. 
All  these  tissues  agree  in  certain  microscopical  and  chemical  characters. 
They,  for  the  most  part,  have  a  large  amount  of  intercellular  substance 
in  which  fibres  are  developed,  and  these  fibres  are  of  two  kinds: — white 
and  yellow  or  elastic.  Moreover,  there  are  many  points  of  similarity 
between  the  cells  which  occur  in  these  several  tissues ;  they  are  all 
developed  from  the  same  embryonic  formation,  and  they  tend  to  pass 
imperceptibly  the  one  into  the  other.  Besides  this,  their  use  is  every- 
where similar;  they  serve  to  connect  and  support  the  other  tissues^ 
performing  thus  a  passive  mechanical  function.  They  may  therefore  be 
grouped  together,  although  differing  considerably  in  external  characters. 
Of  these  connective  tissues,  however,  there  are  three  which  are  so 
intimately  allied  as  to  be  naturally  considered  together,  being  composed 
of  exactly  the  same  elements,  although  differing  in  the  relative  develop- 
ment of  those  elements ;  these  are  the  areolar,  elastic,  and  fibrous 
tissues.  Adipose  tissue  and  retiform  tissue  may  both  be  looked  upon 
as  special  modifications  of  areolar  tissue.  Areolar  tissue  being  the 
commonest  and,  in  a  sense,  the  most  typical,  its  structure  may  be 
considered  first. 


FIG.  39. — GROUND  SUBSTANCE  OF 

FIG.  38. — BUNDLES  OF  THE  WHITE  FIBRES  OF  AREO-       CONNECTIVE  TISSUE   STAINED 
LAR  TISSUE  PARTLY  UNRAVELLED.     (Sharpey.)  BY  SILVER.      (The  cell-spaces 

are  left  white. ) 

Areolar  tissue. — The  areolar  tissue  presents  to  the  naked  eye  an 
appearance  of  fine  transparent  threads  and  laminae  which  intercross  in 
every  direction  with  one  another,  leaving  intercommunicating  meshes, 
or  areolae,  between  them.  When  examined  with  the  microscope,  these 


AEEOLAE  TISSUE. 


39 


threads  and  fibres  are  seen  to  be  principally  made  up  of  wavy  bundles 
of  exquisitely  fine  transparent  fibres  (white  fibres,  fig.  38).  The  bundles 
run  in  different  directions,  and  may  branch  and  intercommunicate  with 
one  another;  but  the  individual  fibres,  although  they  pass  from  one 
bundle  to  another,  never  branch  or  join  other  fibres.  The  fibres  are 
cemented  together  into  the  bundles  by  a  clear  substance  containing 
mucin,  and  the  same  clear  material  forms  also  the  basis  or  ground- 
substance  of  the  tissue,  in  which  the  bundles  themselves  course,  and  in 
which  also  the  corpuscles  of  the  tissue  lie  embedded.  This  ground- 
substance  between  the  bundles  can  with  difficulty  be  seen  in  the  fresh 
tissue  on  account  of  its  extreme  transparency ;  but  it  can  be  brought  to 
view  by  staining  with  nitrate  of  silver,  as  in  §  4.  The  whole  of  the 
tissue  is  thereby  stained  of  a  brown  colour,  with  the  exception  of  the 
spaces  which  are  occupied  by  the  corpuscles  (cell-spaces,  fig.  39). 


FIG.  40.— ELASTIC  FIBRES  OF  AREOLAR 
TISSUE.  FROM  THE  SUBCUTANEOUS 
TISSUE  OF  THE  RABBIT. 

Besides  the  white  fibres  of  con- 
nective tissue  here  described,  fibres 
of  a  different  kind  (fig.  40)  may  be 
made  out  in  the  preparations ;  these 
are  the  elastic  fibres.  They  are 
especially  well  seen  after  treatment 
with  acetic  acid,  and  after  staining 
with  magenta;  but  they  can  be 
detected  also  in  the  fresh  preparation.  They  are.  characterised  by 


NOID    TISSUE    AT    THE    BASE    OF    THE 

BRAIN.     (From  Toldt.) 


40 


THE  ESSENTIALS  OF  HISTOLOGY. 


their  distinct  outline,  their  straight  course,  the  fact  that  they  never  run 
in  bundles,  but  singly,  and  that  they  branch  and  join  neighbouring 
fibres.  If  broken  by  the  needles  in  making  the  preparation,  the  elastic 
recoil  causes  them  to  curl  up,  especially  near  the  broken  ends.  Besides 
the  microscopical  differences,  the  two  kinds  of  fibres  differ  also  in  their 
chemical  characters.  Thus  the  white  fibres  are  dissolved  by  boiling  in 
water,  and  yield  gelatin ;  whereas  the  substance  of  which  the  elastic 
fibres  are  composed  (elastin)  resists  for  a  long  time  the  action  of  boiling 
water.  Moreover,  the  white  fibres  swell  and  become  indistinct  under 
the  action  of  acetic  acid;  the  elastic  fibres  are  unaltered  by  this  reagent. 
The  bundles  of  white  fibres  which  have  been  swollen  out  by  acid 
sometimes  exhibit  curious  constrictions  (fig.  40).  These  are  due  either 
to  elastic  fibres  coiling  round  the  white  bundles,  or  to  cell-processes 
encircling  them,  or  to  an  investment  or  sheath  which  remains  un- 
broken at  certain  parts,  and  thus  prevents  the  swelling  up  of  the 
bundle  at  these  places. 


FIG.  42. —SUBCUTANEOUS  TISSUE  FROM  A  YOUNG  RABBIT,  PREPARED  AS  DIRECTED 
IN  §  1.     (Highly  magnified.) 

The  white  fibres  are  in  wavy  bundles  ;  the  elastic  fibres  form  an  open  network,    p,  p,  plasma- 
cells  ;  g,  granule-cell ;  c,  c',  lamellar-cells ;  /,  fibrillated-cell. 

The  cells  of  areolar  tissue. — Several  varieties  of  connective-tissue 
cells  are  distinguished,  viz. :  (1)  Flattened  lamellar-cells,  which  are  often 
branched  (fig.  42,  c,  c'),  and  may  be  united  one  to  the  other  by  their 
branches,  as  in  the  cornea,  or  are  unbranched  and  joined  edge  to  edge 


AREOLAR  TISSUE.  41 

like  the  cells  of  an  epithelium  ;  the  cell-spaces  have  in  all  cases  a  similar 
arrangement.  (2)  Plasma-cells  of  Waldeyer  (fig.  42,  p),  which  are  com- 
posed of  a  soft  much-vacuolated  protoplasm,  rarely  flattened,  but  other- 
wise varying  greatly  in  shape  and  size.  (3)  Granule-cells  (g),  usually 
spheroidal  or  ovoidal  in  shape,  and  formed,  like  the  plasma  cells,  of  soft- 
protoplasm,  but  thickly  occupied  with  albuminous  granules,  which  are 
deeply  stained  by  eosine  and  by  most  aniline  dyes.  Migratory  lymph- 
corpuscles  may  also  be  seen  here  and  there  in  the  areolar  tissues  (wander- 
cells).  In  the  middle  coat  of  the  eye  the  connective-tissue  cells  are  filled 
with  granules  of  pigment  (pigment-cells). 

The  cells  lie  in  spaces  in  the  ground-substance  between  the  bundles 
of  white  fibres.  In  some  parts  of  the  connective  tissue  the  white 
bundles  are  developed  to  such  an  extent  as  to  pervade  almost  the 
whole  of  the  ground-substance,  and  then  the  connective-tissue  corpuscles 
become  squeezed  into  the  interstices,  flattened  lamellar  expansions  of 
the  cells  extending  between  the  bundles,  as  in  tendon  (see  next  Lesson). 

The  cells  and  cell-spaces  of  areolar  tissue  come  into  intimate  relation 
with  the  cells  lining  the  lymphatic  vessels  and  small  blood-vessels. 
This  connection  can  best  be  seen  in  silvered  preparations ;  it  will  be 
again  referred  to  in  speaking  of  the  origin  of  the  lymphatics. 


FlG.    43.— A    SMALL    FAT-LOBULE    FROM   THE    SUBCUTANEOUS    TISSUE   OF   THE 
GUINEA-PIG,      (%£-. ) 

a,  small  artery  distributed  to  the  lobule  ;  6,  small  vein  ;  the  capillaries  within  the  lobule 

are  not  visible. 

Adipose  tissue  consists  of  vesicles  filled  with  fat  (figs.  43,  44),  and 
collected  into  lobules,  or  into  tracts  which  accompany  the  small  blood- 
vessels. The  vesicles  are  round  or  oval  in  shape,  except  where  closely 
packed,  when  they  become  polyhedral  from  mutual  compression.  The 
fat-drop  is  contained  within  a  delicate  protoplasmic  envelope  (fig.  44, 
m)  which  is  thickened  at  one  part,  and  here  includes  an  oval  flattened 
nucleus.  The  vesicles  are  supported  partly  by  filaments  of  areolar 
tissue,  but  chiefly  by  a  fine  network  of  capillary  blood-vessels. 


42 


THE  ESSENTIALS  OF  HISTOLOGY. 


The  fat  when  first  formed  is  deposited  within  granular  cells  of  areolar 
tissue  (fig.   45).     It  appears  to   be  produced  by  a  transformation  of 


FlG.    44.— A  FEW    CELLS    FROM    THE   MARGIN   OF   A    FAT-LOBULE. 

ff,  fat-globule  distending  a  fat-cell;  n,  nucleus;  m,  membranous  envelope  of  the  fat-cell; 
c  r,  bunch  of  crystals  within  a  fat-cell ;  c,  capillary  vessel ;  v.  venule ;  c  t,  connective- 
tissue  cell ;  the  fibres  of  the  connective  tissue  are  not  represented. 

albuminous  granules  into  droplets  of  fat.     As  these  droplets  increase  in 
size  they  run  together  into  a  larger  drop,  which  gradually  fills  the  cell 


J 


FIG.  45.— DEPOSITION  OF  FAT  IN  CONNECTIVE- TISSUE  CELLS. 

/,  a  ceil  with  a  few  isolated  fat-droplets  in  its  protoplasm  ;  /',  a  cell  with  a  single  large  and 
several  minute  drops  ;  /",  fusion  of  two  large  drops ;  g,  granular  cell,  not  yet  exhibiting 
any  fat-deposition  ;  c  t,  flat  connective-tissue  corpuscle  ;  c,  c,  network  of  capillaries. 

more  and  more,  swelling  it  out  so  that  the  cell-protoplasm  eventually 
appears  merely  as  the  envelope  of  the  fat-vesicle. 

Fat  is  found  most  abundantly  in  subcutaneous  areolar  tissue,  and 


ADIPOSE  TISSUE. 


43 


under  the  serous  membranes ;  especially  in  some  parts,  as  at  the  back 
of  the  peritoneum  around  the  kidneys,  under  the  epicardium,  and  in 
the  mesentery  and  omentum.  The  yellow  marrow  of  the  bones  is  also 
principally  composed  of  fat.  There  is  no  adipose  tissue  within  the 
cavity  of  the  cranium. 

Retiform  or  reticular  tissue  (figs,  46, 47)is  a  variety  of  connective  tissue 
in  which  the  intercellular  or  ground  substance  has  mostly  disappeared  or 
is  replaced  by  fluid.  There  are  very  few  or  no  elastic  fibres  in  it,  and 
the  white  fibres  and  bundles  of  fibres  form  a  dense  network,  the  meshes 
of  which  vary  in  size,  being'  very  small  and  close  in  some  parts ;  more 


FIG.  46.—  RETIFORM  TISSUE  FROM  A  LYMPHATIC  GLAND,  FROM  A  SECTION  WHICH  HAS 
BEEN  TREATED  IN  THE  MANNER,  DESCRIBED  IN  §  5.     (Moderately  magnified.) 

tr,  a  trabeculum  of  connective  tissue ;  r,  r1,  retiform  tissue,  with  more  open  meshes  at 
r  and  denser  at  r'. 

open  and  like  areolar  tissue  in  other  parts.     In  some  places  where 
the  tigsue  occurs  the  fibres  are  almost  everywhere  enwrapped  by  flat- 


FIG.  47.— PORTION  OF  THE  ABOVE,  MORE  HIGHLY  MAGNIFIED. 

tened  branched  connective-tissue  cells,  and  until  these  are  removed  it  is 
not  easy  to  see  the  fibres. 


44  THE  ESSENTIALS  OF  HISTOLOGY. 

Lymphoid  or  adenoid  tissue  is  retiform  tissue  in  which  the  meshes 
of  the  network  are  largely  occupied  by  lymph-corpuscles.  This  is  by 
far  the  most  common  condition  of  a  retiform  tissue,  and  is  met  with  in 
the  lymphatic  glands  and  allied  structures  (see  Lesson  XXII. ),  and  also 
in  the  tissue  of  the  alimentary  mucous  membrane,  and  in  some  other 
situations. 

Basement  membranes  (membranse  proprise)  are  homogeneous-looking 
membranes,  which  are  found  forming  the  surface-layers  of  connective- 
tissue  expansions  in  many  parts,  especially  where  there  is  a  covering  of 
epithelium,  as  on  mucous  membranes,  in  secreting  glands,  and  else- 
where. They  are  generally  formed  of  flattened  connective-tissue  cells 
joined  together  to  form  a  membrane;  but,  in  some  cases,  they  are 
evidently  formed  not  of  cells,  but  of  condensed  ground-substance,  and 
in  others  they  are  of  an  elastic  nature. 

Jelly-like  connective  tissue,  although  occurring  largely  in  the 
embryo,  is  found  only  in  one  situation  in  the  adult — viz.,  forming  the 
vitreous  humour  of  the  eye.  It  seems  to  be  composed  entirely  of  soft 
ground-substance,  with  cells  scattered  here  and  there  through  it,  and 
with  very  few  fibres,  or  none  at  all.  These  several  varieties  of  con- 
nective tissue  will  be  more  fully  described  in  connection  with  the 
organs  where  they  occur. 


THE  CONNECTIVE  TISSUES.  45 


LESSON   X. 

THE  CONNECTIVE  TISSUES  (continued^. 

ELASTIC   TISSUE,    FIBROUS   TISSUE,    DEVELOPMENT   OF   CONNECTIVE   TISSUE. 

1.  TEASE  out  as  finely  as  possible  a  small  shred  of  elastic  tissue  (ligamentum 
nuchse  of  the  ox  or  ligamenta  subflava  of  man)  in  glycerine  and  water, 
slightly  coloured  by  magenta.  Cover  and  cement  the  preparation.  Note 
the  large  well-defined  fibres  constantly  branching  and  uniting  with  one 
another.  Look  for  transverse  markings  on  the  fibres.  Measure  three  or 
four.  Sketch  a  small  part  of  the  network.  Note  the  existence  of  bundles  of 
white  fibres  amongst  the  elastic  fibres. 

2.  Examine  a  thin  transverse  section  of  ligamentum  nuchae  which  has  been 
hardened  in  2  per  cent,  solution  of  bichromate  of  potash.     The  section  is  to 
be  stained  with  hsematoxyliii  and  mounted  in  Canada  balsam  by  the  usual 
process,1  or  simply  in  glycerine  and  water.     Observe  the  grouping  of  the 
fibres  and  their  angular  shape.     Notice  also  the  nuclei  of  connective-tissue 
cells  amongst  the  fibres.     Sketch  one  or  two  groups. 

3.  Pinch  off  the  end  of  the  tail  of  a  dead  mouse  or  rat,  draw  out  the  long 
silk-like  tendons  and  put  them  into  saline  solution.     Take  two  of  the  longest 
threads  and  stretch  them  along  a  slide,  letting  the  ends  dry  firmly  to  the 
slide  but  keeping  the  middle  part  moist.     Put  a  piece  of  hair  between  them 
and  cover  in  saline  solution.     Observe  with  a  high  power  the  fine  wavy 
fibrillation  of  the  tendon.    Draw.    Now  run  dilute  acetic  acid  (0'75  per  cent.) 
under  the  cover-glass,  watch  the  tendons  where  they  are  becoming  swollen 
by  the  acetic  acid.      Notice  the  oblong  nucleated  cells  coming  into  view 
between  the  tendon  bundles.     Sketch  three  or  four  cells  in  a  row.     Lastly, 
lift  the  cover-glass,  wash  away  the  acid  with  distilled  water,  place  a  drop  of 
Delafield's  hgematoxylin  solution  on  the  tendons,  and  leave  the  preparation 
until  it  is  deeply  stained  ;  then  wash  away  the  logwood  and  mount  the  pre- 
paration in  acidulated  glycerine.     Cement  the  cover-glass  with  gold  size. 

4.  Take  one  or  two  other  pieces  of  tendon,  and,  after  washing  them  in 
distilled  water,  stretch  them  upon  a  slide  as  before,  fixing  the  ends  by 
allowing  them  to  dry  on  to  the  slide.     Put  a  drop  of  nitrate  of  silver  solution 
(1  per  cent.)  011  the  middle  of  the  tendons,  and  leave  it  on  for  five  to  ten  minutes, 
keeping  the  preparation  in  the  dark.     Then  wash  off  the  silver  nitrate  with 
distilled  water,  and  expose  the  slide  to  direct  sunlight.      In  a  very  few 
minutes  the  silvered  part  of  the  tendons  will  be  brown.     As  soon  as  this  is 
the  case,  dehydrate  the  tendons  with  alcohol  in  situ  upon  the  slide,  run  off 
the  alcohol,  and  at  once  put  a  drop  of  clove-oil  on  the  preparation.     In  a 
minute  or  two  the  clove-oil  can  be  replaced  by  Canada  balsam  in  xylol,  arid 
covered. 

5.  Stain  with  magenta  solution l  a  thin  section  of  a  tendon  which  has  been 
hardened  in  70  per  cent,  alcohol.     Mount  in  dilute  glycerine  and  cement  the 
cover-glass  at  once.     Sketch  a  portion  of  the  section  under  a  low  power. 

1  See  Appendix. 


46 


THE  ESSENTIALS  OF  HISTOLOGY. 


Elastic  tissue  is  a  variety  of  connective  tissue  in  which  the  elastic 
fibres  preponderate.  It  is  found  most  characteristically  in  the  liga- 
mentum  nuchae  of  quadrupeds  and  the  ligamenta  subflava  of  the 
vertebrae,  but  the  connective  tissue  of  other  parts  may  also  have  a 
considerable  development  of  elastic  fibres.  It  occurs  also  in  an  almost 
pure  form  in  the  walls  of  the  air-tubes,  and  uniting  the  cartilages  of 
the  larynx.  It  also  enters  largely  into  the  formation  of  the  walls  of 
the  blood-vessels,  especially  the  arteries. 

In  the  ligamentum  nuchae  the  fibres  are  very  large  and  angular 
(fig.  48) ;  they  often  exhibit  cross-markings  or  even  transverse  clefts. 
When  dragged  asunder,  they  break  sharply  across ;  they  constantly 
branch  and  unite,  so  as  to  form  a  close  network.  In  transverse 
section  they  are  seen  to  be  separated  into  small  groups  (fig.  49)  by 
intervening  white  bundles  of  connective  tissue. 


FIG.  49. — CROSS-SECTION  OP  ELASTIC 
FIBRES    FROM     THE     LIGAMENTUM 

NUCH^E  OF   THE  OX. 


FIG.  48. — ELASTIC  FIBRES  FROM  THE  LIGA- 
MENTUM NUCH^E  OF  THE  OX,  SHOWING 
TRANSVERSE  MARKINGS  ON  THE  FIBRES. 

Elastic  tissue  does  not  always  take  the  form  of  fibres,  but  may  occur 
as  membranes  (as  in  the  blood-vessels).  Sometimes  the  fibres  are  very 
small,  but  their  microscopical  and  chemical  characters  are  always  very 
well  marked  (see  p.  40). 

Fibrous  tissue  is  almost  wholly  made  up  of  bundles  of  white  fibres 
running  in  a  determinate  direction.  These  again  are  collected  into 


FIBEOUS  TISSUE. 


47 


larger  bundles,  which  give  the  fibrous  appearance  to  the  tissue.  The 
bundles  are  constantly  uniting  with  one  another  in  their  course,  although 
their  component  fibres  remain  perfectly  distinct. 

The  interspaces  between  the  larger  bundles  are  occupied  by  areolar 
tissue  (fig.  50)  in  which  the  blood-vessels  and  lymphatics  of  the  fibrous^ 


FIG.  50. — PART  OF  A  LARGE  TENDON  IN  TRANSVERSE  SECTION.    (Moderately  magnified.) 

a,  areolar  sheath  of  the  tendon,  with  the  fibres  for  the  most  part  running  transversely,  but 
with  two  or  three  longitudinal  bundles,  6  ;  I,  lymphatic  cleft  in  the  sheath  ;  immediately 
over  it  a  blood-vessel  is  seen  cut  across,  and  on  the  other  side  of  the  figure  a  small  artery 
is  shown  cut  longitudinally  ;  c,  large  septum  of  areolar  tissue  ;  d,  smaller  septum  ;  e,  still 
smaller  septum.  The  irregularly  stellate  bodies  are  the  tendon-cells  in  section. 

tissue  are  conveyed.     The  interstices  between  the  smallest  bundles  are 
occupied  by  rows  of  lamellar  connective-tissue  corpuscles  (tendon-cells), 


FIG.  51.— TENDON  OF  MOUSE'S  TAIL;  SHOWING  CHAINS  OF  CELLS  BETWEEN  THE 
TENDON-BUNDLES.     (175  diameters.) 

whichMrom  being  squeezed  up  between  three  or  more  bundles  become 
flattenedjout  in  two  or  three  directions.  In  transverse  section  the  cells 
appear  somewhat  stellate  (figs.  50,  52),  but  when  seen  on  the  flat  they 


48 


THE  ESSENTIALS  OF  HISTOLOGY. 


appear  lamellar  (fig.  51),  and  from  this  aspect  their  general  shape  is 
square  or  oblong.  They  lie,  as  before  said,  in  rows  between  the  tendon- 
bundles,  and  the  nuclei  of  adjacent  cells  are  placed  opposite  one  another 


FIG.  52.— TRANSVEKSE  SECTION  OF  TENDON  OP 
MOUSE'S  TAIL,  STAINED.  (175  diameters.) 

The  flattened  processes  of  the  tendon-cells  appear 
in  section  as  lines,  frequently  coming  off  at  right 
angles  from  the  body  of  the  cell. 


in  pairs  (fig.  53).     The  cell-spaces  correspond  in  general  figure  and 
arrangement  to  the  cells  which  occupy  them  (fig.  54). 


FIG.  53. — EIGHT  CELLS  FROM  THE  SAME  TENDON  AS  REPRESENTED  IN  FIG.  51. 
(425  diameters.) 

The  dark  lines  on  the  surface  of  the  cells  are  the  optical  sections  of  lamellar  extensions 
directed  towards  or  away  from  the  observer. 

Fibrous  tissue  forms  the  tendons  and  ligaments,  and  also  certain 
membranes,  such  as  the  dura  mater,  the  fibrous  pericardium,  the  fasciae 
of  the  limbs,  the  fibrous  covering  of  certain  organs,  etc.  It  is  found 
wherever  great  strength  combined  with  flexibility  is  concerned.  It 


FIG.  54.— CELL- SPACES  OF  TENDON  OF  MOUSE'S  TAIL,  BROUGHT  INTO  VIEW  BY 

TREATMENT  WITH  NITRATE  OF  SILVER.      (175  diameters.) 

receives  a  few  blood-vessels,  disposed  longitudinally  for  the  most  part, 
and  contains  many  lymphatics.  Tendons  and  ligaments  also  receive 
nerve-fibres,  which,  in  some  cases,  end  in  small  localised  ramifications 
like  the  end-plates  of  muscle,  while  others  terminate  in  end-bulbs  or  in 
simple  Pacinian  corpuscles.  These  will  be  described  along  with  the 
modes  of  ending  of  nerve-fibres. 

Development   of  connective   tissue. — Connective   tissue  is  always 
developed  in  the  mesoblast  or  mesoderm  of  the  embryo.     In  those 


FIBROUS  TISSUE:  49 

parts  of  this  layer  which  are  to  form  connective  tissue,  the  embryonic 


FIG.  55. — JELLY  OP  WHARTON.    (Kanvier.) 

r,  ramified  cells  intercommunicating  by  their  branches  ;  I,  a  row  of  lymph  cells  ; 
/,  fibres  developing  in  the  ground-substance. 

cells  become  separated  from  one  another  by  a  muco-albuminous  semi 
fluid  intercellular  substance  (ground-substance),  but  the  cells  generally 
remain  connected  by  their 
processes.  The  connective- 
tissue  fibres,  both  white 
and  elastic,  are  deposited  in 
this  ground-substance,  the 
elastic  substance  usually  in 
the  form  of  granules  (fig. 
56,  g),  which  subsequently 
become  connected  together 
into  elastic  fibres  or  laminae, 
as  the  case  may  be,  the 
white  fibres  appearing  at 
first  in  the  form  of  very 
fine  bundles,  which  after- 
wards become  gradually 
larger;  so  that  in  fibrous 
tissue  the  whole  ground-substance  is  eventually  pervaded  by  them,  and 
the  cells  of  the  tissue  become  squeezed  up  into  the  intervals  between 
them.  Before  any  considerable  development  of  fibres  has  taken  place, 
the  embryonic  connective  tissue  has  a  jelly-like  appearance ;  in  this 
form  it  occurs  in  the  umbilical  cord,  where  it  is  known  as  the  jetty  of 
Wlmrton  (fig.  55). 


FIG.  56.— DEVELOPMENT  OF  ELASTIC  TISSUE  BY 
DEPOSITION  OF  FINE  GRANULES.     (Ranvier.) 

,  fibres  being  formed  of  rows  of  '  elastin '  granules  ; 
p,  flat  plate-like  expansion  of  elastic  substance 
formed  by  the  fusion  of  '  elastin  '  granules. 


50  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  XL 

THE  CONNECTIVE  TISSUES  (continued). 

ARTICULAR  CARTILAGE. 

1.  COT  two  or  three  very  thin  tangential  slices  of  the  fresh  cartilage  of  a  joint, 
mount  them  in  saline  solution  or  serum,  and  examine  with  a  high  power. 
Observe  carefully  the  form  and  grouping  of  the  cells.  Look  at  the  thin  edge 
of  the  section  for  spaces  from  which  the  cells  have  dropped  out.  Measure 
two  or  three  cells  and  their  nuclei,  and  sketch  one  or  two  groups.  Now 
replace  the  saline  solution  by  water  and  set  the  preparation  aside  for  a  little 
while.  On  again  examining  it,  many  of  the  cartilage-cells  will  be  found  to 
have  shrunk  away  from  their  containing  capsules.  . 

2.  Make  other  sections  of  the  cartilage  (1)  from  near  the  middle,  (2)  from 
near  the  edge.     Place  the  sections  for  two  or  three  minutes  in  acetic  acid 
(1  per  cent.),  wash  them  with  water,  and  stain  with  dilute  haematoxylin 
solution.     When  stained  mount  in  dilute  glycerine  and  cement  the  cover- 
glass.     In  (2)  look  for  branched  cartilage-cells.     Draw  one  or  two. 

3.  Make  vertical  sections  of   articular  cartilage  from  a  bone  which   has 
been  for  several  days  in  £  per  cent,  chromic  acid  solution,  and  mount  the 
sections   in   glycerine   and  water,    or,   after   staining,    in   Canada   balsam.1 
Sketch  the  arrangement  of  the  cells  in  the  different  layers. 

4.  Wash  a  fresh  joint  with  distilled  water  ;  drop  1  per  cent,  nitrate  of  silver 
solution  over  it ;  after  five  to  ten  minutes  wash  away  the  nitrate  of  silver 
and  expose  in  water  to  direct  sunlight.     When  browned,  place  in  spirit  for 
half  an  hour  or  more,  and  then  with  a  razor  wetted  with  spirit  cut  thin 
sections  from  the  surface  and  mount  in  Canada  balsam  after  passing  through 
clove-oil.     The   cells   and    cell-spaces   show   white   in   the    brown   ground- 
substance.     Draw. 


Cartilage  or  gristle  is  a  translucent  bluish-white  tissue,  firm,  and  at 
the  same  time  elastic,  and  for  the  most  part  found  in  connection  with 
bones  of  the  skeleton,  most  of  which  are  in  the  embryo  at  first  repre- 
sented entirely  by  cartilage.  Two  chief  varieties  of  cartilage  are 
distinguished.  In  the  one,  which  is  termed  hyaline,  the  matrix  or 
ground-substance  is  clear,  and  free  from  obvious  fibres ;  in  the  other, 
which  is  termed  fbro-carlilage,  the  matrix  is  everywhere  pervaded  by 
connective-tissue  fibres.  When  these  are  of  the  white  variety,  the 
tissue  is  white  fibro-cartilage  ;  when  they  are  elastic  fibres,  it  is  yellow  or 
elastic  jibro-cartilage. 

1  See  Appendix. 


HYALINE  CARTILAGE.  51 

Hyaline  cartilage  occurs  principally  in  two  situations — namely  (1) 
covering  the  ends  of  the  bones  in  the  joints,  where  it  is  known  as 
articular  cartilage  ;  and  (2)  forming  the  rib-cartilages,  where  it  is  known 
as  costal  cartilage.  It  also  forms  the  cartilages  of  the  nose,  the  external 
auditory  meatus,  the  larynx,  and  the  windpipe  ;  in  these  places  it  serves 
to  maintain  the  shape  and  patency  of  the  orifices  and  tubes. 

Articular  cartilage. — The  cells  of  articular  cartilage  are  mostly 
scattered  in  groups  of  two  or  four  throughout  the-  matrix  (fig.  57). 
The  latter  is  free  from  fibres,  except  at  the  extreme  edge  of  the 


FIG.  57.— ARTICULAR  CARTILAGE  FROM  HEAD  OF  METATARSAL  BONE  OF  MAN 
(OSMIC  ACID  PREPARATION).  THE  CELL-BODIES  ENTIRELY  FILL  THE  SPACES 
IN  THE  MATRIX.  (340  diameters. ) 

a,  group  of  two  cells ;  b,  group  of  four  cells  ;  h,  protoplasm  of  cell,  with  y,  fatty  granules  ; 

n,  nucleus. 

cartilage,  where  the  connective-tissue  fibres  from  the  synovial  membrane 
extend  into  it ;  and  here  also  the  cartilage-cells  are  often  branched,  and 
offer  transitions  to  the  branched  connective-tissue  corpuscles  of  that 
membrane  (transitional  cartilage,  fig.  58).  By  long  maceration,  however, 
evidence  of  a  fibrous  structure  may  be  obtained,  even  in  the  matrix  of 
true  hyaline  cartilage.  Some  histologists  also  describe  fine  communica- 
tions in  the  matrix  uniting  the  cartilage-cells  with  one  another,  but 
these  are  of  doubtful  occurrence. 


52  THE  ESSENTIALS  OF  HISTOLOGY. 

The  matrix  immediately  around  the  cartilage-cells  is  often  marked 
off  from  the  rest  by  a  concentric  line  or  lines,  this  part  of  the  matrix, 

a  I 


FIG.  58.— BORDER  OF  ARTICULAR  CARTILAGE  SHOWING   FIG.  59.— A  CARTILAGE-CELL 

TRANSITION   OF   CARTILAGE   CELLS   INTO   CONNECTIVE-  IN     THE     LIVING     STATE, 

TISSUE  CORPUSCLES   OF  SYNOVIAL  MEMBRANE.      FROM  FROM    THE    SALAMANDER. 

HEAD  OF  METATARSAL  BONE,  HUMAN.      (About  340  (Flemming.)  (Very highly 

diameters. )  magnified. ) 

or.,  ordinary  cartilage-cells ;  6,  6,  with  branching  processes. 

which  is  the  latest  formed,  being  known  as  the  capsule  of  the  cell     The 
cells  are  bluntly  angular  in  form,  the  sides  opposite  to  one  another  in 


FIG.  60.— VERTICAL  SECTION  OF  ARTICULAR  CARTILAGE  COVERING  THE  LOWER  END 
OF  THE  TIBIA,  HUMAN.     (Magnified  about  30  diameters. ) 

a,  cells  ana  cell-groups  flattened  conformably  with  the  surface ;  b,  cell-groups  irregularly 
arranged  ;  c,  cell-groxips  disposed  perpendicularly  to  the  surface  ;  d,  layer  of  calcined 
cartilage  ;  e,  bone. 

the  groups  being  generally  flattened.     The  protoplasm  is  very  clear, 
but  it  may  contain  droplets  of  fat ;  and  with  a  high  power  fine  inter- 


ARTICULAR  CARTILAGE. 


53 


lacing  filaments  and  granules  have  been  observed  in  it  (fig.  59).  During 
life  the  protoplasm  entirely  fills  the  cavity  or  cell-space  which  it 
occupies  in  the  matrix;  but  after  death,  and  in  consequence  of  the 
action  of  water  and  other  agents,  it  tends  to  shrink  away  from  the 
capsule.  The  nucleus  is  round,  and  shows  the  usual  intranuclear 
network. 

In  vertical  section  (fig.  60)  the  deeper  cell-groups  (c)  are  seen  to  be 
arranged  vertically  to  the  surface,  the  more  superficial  ones  (a)  parallel 
to  the  surface ;  whilst  in  an  intermediate  zone  the  groups  are  irregu- 
larly disposed  (b).  In  the  deepest  part  of  the  cartilage,  next  the  bone, 
there  is  often  a  deposition  of  calcareous  salts  in  the  matrix  (calcified 
cartilage,  d). 

The  disposition  of  the  cells  of  cartilage  in  groups  of  two,  four,  and 
so  on,  is  apparently  due  to  the  fact  that  these  groups  have  originated 
from  the  division  of  a  single  cell  first  into  two,  and  these  again  into 
two,  and  so  on  (fig.  61).  It  would  seem  that  the  matrix  is  formed  of 


B  c 


ill 


FIG.  01.  —  PLAN  OF  THE  MULTIPLICATION  OF  CELLS  OF  CARTILAGE.    (Sharpey.) 

A,  cell  in  its  capsule  ;  B,  divided  into  two,  each  with  a  capsule;  c,  primary  capsule,  dis- 
appeared, secondary  capsules  coherent  with  matrix  :  D,  tertiary  division  ;  E,  secondary 
capsules  disappeared,  tertiary  coherent  with  matrix. 

successive  portions,  which  are  deposited  around  each  cartilage-cell  as 
the  so-called  '  capsules,'  each  newly  formed  portion  soon  blending  in  its 
turn  with  the  previously  formed  matrix,  whilst  a  new  capsule  is  formed 
within  it.  The  division  of  the  cartilage-cell,  like  that  of  other  cells, 
is  accompanied  by  a  process  of  karyokinesis. 

Embryonic  cartilage  is  characterised  by  the  cells  being  usually  more 
sharply  angular  and  irregular,  being  even  in  some  cases,  markedly 
branched,  like  those  which  occur  at  the  junction  of  cartilage  and  synovial 
membrane  in  the  adult.  The  cells  are  also  more  closely  packed,  the 
matrix  being  in  relatively  less  amount. 


THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  XII. 

THE  CONNECTIVE  TISSUES  (continued}. 

• 

COSTAL  CARTILAGE.       FIBRO-CARTILAGE. 

1.  MAKE  transverse  and  tangential  sections  of  a  rib-cartilage,  which  may 
either  be  fresh,  or  may  have  been  preserved  in  spirit.  Stain  them  with 
haematoxylin  (if  fresh,  after  treatment  with  acetic  acid  as  in  Lesson  XL, 
§  2),  and  mount  in  glycerine.  Sketch  a  part  of  a  transverse  section  under 
a  low  power  and  a  cell-group  from  one  of  the  tangential  sections  under  a 
high  power.  Notice  especially  the  arrangement  of  the  cells,  somewhat  con- 
centric near  the  surface  but  radial  near  the  centre.  The  costal  cartilages 
are  often  ossified  near  the  middle  in  animals,  but  in  man  when  ossification 
occurs  it  is  the  superficial  layer  which  is  invaded. 

2.  Make  sections  of  the  cartilage  of  the  external  ear,  either  fresh  or  after 
hardening  in  alcohol.      Mount   in    dilute   glycerine   faintly  coloured   with 
magenta.     If  from  the  ox,  notice  the  very  large  reticulating  elastic  fibres  in 
the  matrix.     Notice  also  the  isolated  granules  of  elastin,  and  around  the 
cartilage-cells  the  area  of  clear  ground-substance.     Draw  a  small  portion  of 
the  section. 

3.  Mount  a  section  of  the  epiglottis  in  the  same  way.     Notice  the  closer 
network  of  much  finer  fibres  in  its  cartilage. 

4.  Cut  sections  of  white  fibro-cartilage  (intervertebral  disk),  which  has 
been  hardened  in  saturated  solution  of  picric  acid,  followed  by  spirit,  or  in 
spirit  only.     Stain  the  sections  with  -dilute  hsematoxylin.     Mount  in  dilute 
glycerine.     Observe  the  wavy  fibres  in  the  matrix  and  the  cartilage-cells 
lying  in  clear  areas  often  concentrically  striated.     Look  for  branched  carti- 
lage-cells.    Sketch  three  or  four  cells  and  the  adjoining  fibrous  matrix. 


Costal  cartilage. — In  the  costal  cartilages  the  matrix  is  not  always 
so  clear  as  in  the  cartilage  of  the  joints,  for  it  often  happens  that  fibres 
become  developed  in  it.  The  cells  are  generally  larger  and  more 
angular  than  those  of  articular  cartilage,  and  collected  into  larger 
groups  (fig.  62).  Near  the  circumference,  and  under  the  perichondrium 
or  fibrous  covering  of  the  cartilage,  they  are  flattened  and  parallel  to 
the  surface,  but  in  the  deeper  parts  they  have  a  more  irregular  or  a 
radiated  arrangement.  They  frequently  contain  fat.  The  cartilages  of 
the  larynx  and  windpipe  and  of  the  nose  resemble  on  the  whole  the 
costal  cartilages,  but  the  study  of  them  may  be  deferred  until  the 
organs  where  they  occur  are  dealt  with. 


FIBRO-CARTILAGE.  55, 

Elastic  or  yellow  fibro-cartilage  occurs  in  only  a  few  situations. 
These  are,  the  cartilage  of  the  external  ear  and  that  of  the  Eustachian 
tube,  and  the  epiglottis  and  cartilages  of  Santorini  of  the  larynx.  The 


FIG.  62. — SECTION  OF  RIB-CARTILAGE,  SHOWING  CELLS  AND  CELL-GROUPS  IN  A 

SOMEWHAT  FIBROUS-LOOKING  MATRIX. 

Two  or  three  empty  cell-spaces  are  seen  from  which  the  cells  have  dropped  out  in  preparing 

the  section. 

matrix  is  everywhere  pervaded  with  well-defined  branching  fibres, 
which  unite  with  one  another  to  form  a  close  network  (fig.  63).  These 
fibres  resist  the  action  of  acetic  acid,  and  are  stained  deeply  by  magenta ; 
they  are  evidently  elastic  fibres.  In  the  ox  they  are  very  large,  but 
smaller  in  man,  especially  in  the  cartilage  of  the  epiglottis  (fig.  64). 
They  appear  to  be  developed,  as  with  elastic  tissue  elsewhere  (see  p.  49), 
by  the  deposition  of  granules  of  elastin  in  the  matrix,  which  at  first  lie 
singly,  but  afterwards  become  joined  to  form  the  fibres. 

White  fibro-cartilage  is  found  wherever  great  strength  combined 
with  a  certain  amount  of  rigidity  is  required  :  thus  we  frequently  find 
fibro-cartilage  joining  bones  together,  as  in  the  case  of  the  intervertebral 
disks  and  other  symphyses.  Fibro-cartilage  is  frequently  employed  to 
line  grooves  in  which  tendons  run,  and  it  may  also  be  found  in  the 
tendons  themselves.  It  is  also  employed  to  deepen  cup-shaped  articular 
surfaces  ;  and  in  the  case  of  the  interarticular  cartilages,  such  as  those 
of  the  knee  and  lower  jaw,  to  allow  greater  freedom  of  movement 
whilst  diminishing  the  liability  to  dislocation.  Under  the  microscope 
white  fibro-cartilage  looks  very  like  fibrous  tissue,  but  its  cells  are 


56 


THE  ESSENTIALS  OF  HISTOLOGY. 


cartilage-,  not  tendon-,  cells  (fig.  65).     They  are  rounded  or  bluntly 
angular  and   surrounded   by  a   concentrically  striated   area   of   clear 


FIG.  64.  —SECTION  OF  PART  OF  THE  CARTI- 
LAGE OF  THE  EPIGLOTTIS.     (Ranvier.) 
a,  cartilage  cell  in  clear  area ;  b,  granular-looking 

FIG.  (5o.—  SECTION  OF  THE  ELASTIC  CARTI-  matrix  near  the  middle  of  the  cartilage,  the 
LAGE  OF  THE  EAR.  (Hertwig.)  (Highly  granular  appearance  being  due  partly  to  the 
magnified.)  nne  reticulum  of  elastic  fibres,  partly  to  the 

presence  of  granules  of  elastic  substance  in  the 
matrix ;  c,  clearer  matrix  with  longer  fibres. 

cartilage-matrix.     In  some  parts  of  the  intervertebral  disk  many  of  the 


FIG.  65.— WHITE  FIBHO-CARTILAGE  FROM  AN  INTERVERTEBRAL  DISK,  HUMAN. 
(Highly  magnified.) 

The  concentric  lines  around  the  cells  indicate  the  limits  of  deposit  of  successive  capsules. 
One  of  the  cells  has  a  forked  process  which  extends  beyond  the  hyaline  area  surround- 
ing the  cell,  amongst  the  fibres  of  the  general  matrix. 

cells  are  branched,  and  may  be  looked  upon  as  transitional  forms  to 
connective-tissue  corpuscles. 


BONE  AND  MARROW.  57 


LESSON  XIII. 


BONE  AND  MARROW. 

1.  IN  thin  sections  of  hard  bone  made  by  grinding,  observe  the  Haversian 
canals,  lamellae,  lacunae,  canaliculi,  etc.  Make  a  sketch  first  under  a  low  and 
afterwards  under  a  high  power. 

2.  With  fine  forceps  strip  off  a  thin  shred  from  the  superficial  layers  of  a 
bone  which  has  been  decalcified  in  dilute  nitric  acid  and  afterwards  kept  for 
some  time  in  dilute  alcohol.    Mount  the  shred  in  water.     Observe  the  fibrous 
structure  of  the  lamellae.     Look  for  perforating  fibres  or  the  holes  from 
which  they  have  been  dragged  out.     Sketch  a  small  piece  of  the  thin  edge  of 
a  lamella. 

3.  Stain  with  dilute  magenta  very  thin  sections  of  compact  bone  which 
has  been  decalcified  in  chromic  or  picric  acid,  and  mount  in  dilute  glycerine, 
cementing  at  once.     Look  for  fibres  of  Sharpey  piercing  the  circumferential 
lamellae.     The  elastic  perforating  fibres  are  more  darkly  stained  than  the 
others.     Notice  the  stained  nuclei  of  the  bone-corpuscles  in  the  lacunae.     In 
the  thinnest  parts  of  the  sections  try  to  make  out  the  blood-vessels  and  other 
structures  in  the  Haversian  canals. 

4.  Mount  in  Canada  balsam  sections  of  marrow  (from  a  long  bone  of  a 
rabbit)  stained   with   haematoxylin.1      Observe   the   fat-cells,  the   reticular 
tissue  supporting  them,  the  proper  marrow-cells  in  this  tissue,  etc. 

5.  Tease  in  salt  solution  or  serum  some  of  the  red  marrow  from  the  rib  of  a 
recently  killed  animal.      Observe  and  sketch  the  proper  marrow-cells  and 
look  for  myeloplaxes  and  nucleated  coloured  blood-corpuscles.     If  examined 
carefully,  amoeboid  movements  may  be  detected  in  the  latter  and  in  the 
marrow-cells. 


Bone  is  a  connective  tissue  in  which  the  ground-substance  is  im- 
pregnated with  salts  of  lime,  chiefly  phosphate,  these  salts  constituting 
about  two-thirds  of  the  weight  of  the  bone.  When  bones  are  macerated 
this  earthy  matter  prevents  the  putrefaction  of  the  animal  matter. 
When  bones  are  calcined  they  lose  one-third  of  their  weight,  owing  to 
the  destruction  of  the  animal  matter ;  when  steeped  in  acid  the  earthy 
salts  are  dissolved  and  only  the  animal  matter  is  left.  This,  like 
areolar  and  fibrous  tissue,  is  converted  into  gelatine  by  boiling. 

Bony  tissue  is  either  compact  or  cancellated.  Compact  bone  is  dense 
like  ivory ;  cancellated  is  spongy  with  obvious  interstices.  The  outer 
layers  of  all  bones  are  compact,  and  the  inner  part  is  generally  can- 

1  See  Appendix. 


58  THE  ESSENTIALS  OF  HISTOLOGY. 

cellated,  but  the  shaft  of  a  long  bone  is  almost  entirely  made  up  of 
compact  substance  except  along  the  centre,  which  is  hollow  and  filled 
with  marrow.  The  interstices  of  cancellated  bone  are  also  occupied 
by  marrow.  Externally  bones  are  covered  except  at  the  joints  by  a 
vascular  fibrous  membrane,  the  periosteum. 

True  bone  is  always  made  up  of  lamella,  and  these  again  are  com- 
posed of  fine  fibres  lying  in  a  calcified  ground-substance.  Between  the 
lamellae  are  branched  cells,  the  bone-corpuscles,  which  lie  in  cell-spaces 
or  lacunce.  The  ramified  passages  which  contain  the  cell-processes  are 
termed  canaliculi. 

In  cancellated  bone  the  blood-vessels  run  in  the  interstices  supported 
by  the  marrow.  In  compact  bone  they  are  contained  in  little  canals — 
the  Haversian  canals — which  everywhere  pervade  the  bone.  These 
canals  are  about  O05  mm.  (-^  inch)  in  diameter,  but  some  are 


FIG.  66. — TRANSVERSE  SECTION  OF  A  BONE  (ULNA).      (Sharpey.)     (Magnified 
20  diameters.) 

The  openings  of  the  Haversian  canals  are  seen  encircled  by  concentric  lamellae.     Other  lamella-: 
run  parallel  with  the  surface  (a). 

smaller,  others  larger  than  this.  Their  general  direction  is  longitudinal. 
i.e.  parallel  to  the  long  axis  of  the  bone,  but  they  are  constantly  united 
by  transversely  and  obliquely  running  passages.  In  a  section  across 


BONE.  59 

the  shaft  of  a  long  bone  they  are  seen  as  small  rounded  or  irregular 
holes  (fig.  66).  When  the  section  has  been  made  by  grinding,  the 
holes  get  filled  up  with  air  and  debris,  and  they  then  look  black  by 
transmitted  light,  as  do  also  the  lacunae  and  canaliculi  (fig.  67).  Most 
of  the  lamellae  in  compact  bone  are  disposed  concentrically  around  the 
Haversian  canals ;  they  are  known  as  the  Haversian  lamellae,  and  with 


FIG.  67. — TKANSVEESE  SECTION  OF  COMPACT  TISSUE  (OP  HUMEEUS.)    (Sharpey.) 
(Magnified  about  150  diameters.) 

Three  of  the  Haversian  canals  are  seen,  with  their  concentric  rings ;  also  the  lacunse,  with 
the  canaliculi  extending  from  them  across  the  direction  of  the  lamellee.  The  Haversian 
apertures  had  become  filled  with  air  and  debris  in  grinding  down  the  section,  and  therefore 
appear  black  in  the  figure,  which  represents  the  object  as  viewed  with  transmitted  light. 

the  included  canal  form  what  is  known  as  a  Haversian  system.  The 
lacunae  of  a  Haversian  system  communicate  with  one  another  and 
with  the  Haversian  canal,  but  not  as  a  rule  with  the  lacunae  of  other 
Haversian  systems.  The  angular  interstices  between  the  Haversian 
systems  are  generally  occupied  by  bony  substance,  which  is  fibrous  but 
not  lamellar.  Besides  the  lamellae  of  the  Haversian  systems  there  is  a 
certain  thickness  of  bone  at  the  surface,  immediately  underneath  the 
periosteum,  which  is  composed  of  lamellae  arranged  parallel  with  the 
surface ;  these  are  the  circumferential  or  periosteal  lamellce  (fig.  66,  a). 
They  are  pierced  here  and  there  by  canals  for  blood-vessels,  which  are 
proceeding  from  the  periosteum  to  join  the  system  of  Haversian  canals, 
and  also  by  calcified  bundles  of  white  fibres  and  by  elastic  fibres  which 
may  also  be  prolonged  from  the  periosteum.  These  are  the  perforating 
fibres  of  Sharpey  (fig.  68). 

The  lamellae  of  bone  are  fibrous  in  structure.     This  may  be  seen  in 
shreds  torn  off  from  the  superficial  layers  of  a  decalcified  bone  (fig 


60 


THE  ESSENTIALS  OF  HISTOLOGY. 

c 


FIG.  68.— TBANS VERSE  SECTION  OP  DECALCIFIED  HUMAN  TIBIA,  PEOM  NEAR  THE 

SURFACE  OF  THE  SHAFT. 

ii,  H,  Haversian  canals,  with  their  systems  of  concentric  lamellse ;  in  all  the  rest  of  the  figure 
the  lamellae  are  circumferential ;  s,  ordinary  perforating  fibres  of  Sharpey ;  e,  e,  elastic 
perforating  fibres.  Drawn  under  a  power  of  about  150  diameters. 


FIG.  69.— LAMELLA  TORN  OFF  FROM  A  DECALCIFIED  HUMAN  PARIETAL  BONE  AT 

SOME  DEPTH  FROM  THE  SURFACE.   (Sharpey.) 

a,  lamellae,  showing  decussating  fibres ;  b,  b,  thicker  part,  where  several  lamellse  are  super- 
posed ;  c,  c,  perforating  fibres ;  the  fibrils  which  compose  them  are  not  shown  in  the 
figure.  Apertures  through  which  perforating  fibres  had  passed  are  seen,  especially  in  the 
lower  part,  a,  a,  of  the  figure.  Magnitude  as  seen  under  a  power  of  200,  but  not  drawn  to 
a  scale.  (From  a  sketch  by  Allen  Thomson.) 


BONE.  61 

69).  The  fibres  often  cross  one  another  in  adjacent  lamellae,  and  in 
the  Haversian  systems  they  run  in  some  lamellae  concentrically,  in 
others  parallel  with  the  Haversian  canal.  In  shreds  of  lamellae  which 
have  been  peeled  off  from  the  surface  the  perforating  fibres  may  some- 
times be  seen  projecting  from  the  surface  of  the  shred,  having  been 
torn  out  of  the  deeper  lamellae  (fig.  69,  c,  c).  Where  tendons  or  liga- 
ments are  inserted  into  bone,  their  bundles  of  white  fibres  are  prolonged 
into  the  bone  as  perforating  fibres. 

The  lacunae  are  occupied  by  nucleated  corpuscles,  which  send  branches 
along  the  canaliculi  (fig.  70). 

The  Haversian  canals  contain  one  or  two  blood-capillaries  and 
nervous  filaments,  besides  a  little  connective  tissue;  and  the  larger 


Tlotenh  f™        FlG'  71'-SECTION  OF  A  HAVERSIAN  CANAL, 

(Joseph.)  SHOWING  ITS  CONTENTS.     (Highly 

a,  proper  wall  of  the  lacuna,  where  the  corpuscle  magnified. ) 

has  shrunken  away  from  it.  ,,      ,     .  ,        .,, 

a,  small  arterial  capillary  vessel ;  v,  large  venous 
capillary;  n,  pale  nerve-fibres  cut  across;  Z, 

Ones    may    also    Contain  a  few  mar-       cleft-like  lymphatic  vessel ;    one  of  the  cells 

forming  its  wall  communicates  by  fine  branches 

rOW-CellS.         I  here    are     also     Clett-       with  the  branches  of  a  bone-corpuscle.     The 

.  .  .  ,         substance  in  which  the  vessels  run  is  connec- 

llke  lymphatic  Spaces  running  With        tive    tissue    with    ramified    cells ;    its    finely 

,  ,  iii         granular  appearance   is  probably  due   to  the 

the  vessels  and  Connected  through       cross-section  of    fibrils.      The    canal    is    sur- 

,.      ,.       ..,11  -I         f  rounded  by  several  concentric  lamella?. 

canaliculi  with  branches  from  cor- 
puscles  within   the   neighbouring   lacunae    of    the    osseous   substance 
(fig.  71). 

The  periosteum  (which  is  studied  in  torn-off  shreds,  in  preparations 
stained  in  situ  with  silver  nitrate,  and  in  logwood-stained  sections  from 
a  bone  which  has  been  decalcified  in  chromic  or  picric  acid)  is  a  fibrous 
membrane  composed  of  two  layers,  the  inner  of  which  contains  many 
elastic  fibres.  In  the  outer  layer  numerous  blood-vessels  ramify  and 
send  from  it  branches  to  the  Haversian  canals  of  the  bone.  The 
periosteum  ministers  to  the  nutrition  of  the  bone,  partly  on  account  of 
the  blood-vessels  arid  lymphatics  it  contains,  partly,  especially  in  young 
animals,  on  account  of  the  existence  between  it  and  the  bone  of  a  layer 


62 


THE  ESSENTIALS  OF  HISTOLOGY. 


of  osteoblasts  or  lone-forming  cells,  a  remainder  of  those  which  originally 
produced  the  bone. 

The  marrow  of  bone  is  of  a  yellow  colour  in  the  shafts  of  the  long 
bones,  and  is  there  largely  composed  of  adipose  tissue,  but  in  the  can- 
cellated tissue  it  is  usually  red,  the  colour  being  partly  due  to  the  large 
amount  of  blood  in  its  vessels.  This  red  marrow  is  chiefly  composed  of 
round  nucleated  cells — the  marrow-cells  (tig.  72,e-i) — which  resemble  large 
lymph-corpuscles,  and,  like  these,  are  amoeboid.  There  are  also  to  be 
seen  mingled  with  them  a  number  of  corpuscles  somewhat  smaller  in 
size,  but  nucleated  and  amoeboid,  and  of  a  reddish  tint  (fig.  72,  j-t). 
These  cells,  which  are  termed  erythroblasts,  resemble  the  nucleated 


FIG.  72.— CELLS  OF  THE  RED  HARROW  OF  THE  GUINEA-PIG.     (Highly  magnified.) 

«,  a  large  cell,  the  nucleus  of  which  appears  to  be  partly  divided  into  three  by  constrictions  ; 
b,  a  cell  the  enlarged  nucleus  of  which  shows  an  appearance  of  being  constricted  into  a 
number  of  smaller  nuclei ;  c,  a  so-called  giant-cell  or  myeloplaxe  with  many  nuclei  ;  d,  a 
smaller  myeloplaxe  with  three  nuclei ;  e-i,  proper  cells  of  the  marrow  ;  j-t,  various  forms  of 
coloured  nucleated  cells,  some  in  process  of  division. 

coloured  blood-corpuscles  of  the  embryo,  and  they  are  believed  to  be 
cells  from  which  the  coloured  blood-disks  become  developed  (Neumann). 
Many  of  them  are  in  process  of  division  by  karyokinesis,  and  others  are 
seen  with  the  nucleus  in  a  more  or  less  atrophied  condition ;  from 
which  it  may  be  inferred  that  the  transformation  into  a  discoid  blood- 
corpuscle  is  accompanied  by  the  disappearance  of  the  nucleus 
(Bizzozero).  Lastly  the  marrow  contains  a  certain  number  of  very 
large  cells  with  multiple  nuclei,  the  myeloplaxes  of  Robin  (fig.  72, 
a,  b,  c,  d).  These  are  especially  numerous  wherever  bone  is  becoming 
absorbed,  but  are  not  confined  to  such  situations,  being  indeed  normal 
constituents  of  marrow.  Sometimes,  instead  of  possessing  several 


MARROW.  63 

nuclei,  these  cells  contain  but  one  large  nucleus,  which  then  usually 
shows  an  appearance  as  of  budding  (b).  Lastly,  the  existence  of  cells 
within  the  marrow  containing  blood-corpuscles  in  various  stages  of 
transformation  into  pigment,  similar  to  those  which  occur  in  the  spleen 
pulp,  has  also  been  affirmed  (by  Osier).  The  marrow  is  very  vascular, 
the  capillaries  and  veins  being  large  and  thin-walled ;  indeed,  according 
to  some  authorities,  the  walls  of  the  capillaries  are  imperfect,  so  that 
there  is  an  open  communication  between  them  and  the  interstices  of 
the  tissue,  and  in  this  way  it  is  supposed  that  the  coloured  blood-disks, 
which  are  believed  to  be  produced  from  the  coloured  nucleated  cells  of 
the  marrow,  may  get  into  the  circulation. 


64  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  XIV. 

DEVELOPMENT  OF  BONE. 

1.  MOUNT  in  Canada  balsam  a  section  of  a  foetal  lower  jaw  which  has  been 
stained  in  bulk  with  magenta  or  hsematoxylin  and  embedded  in  paraffin.1 
Find  the  part  where  the  lower  jaw-bone  is  becoming  ossified,  and  carefully 
study  the  appearance  which  it  presents.  The  bone  is  prolonged  in  the  form 
of  osteogenic  fibres  which  are  covered  with  osteoblasts. 

2.  Intramembranous  ossification  may  also  be  studied  in  the  parietal  bone 
of  a  foetus  which  has  been  preserved  in  Miiller's  fluid.     A  piece  of  the  growing 
edge  is  scraped  or  brushed  free  from  its  investing  membranes,  and  from  most 
of  the  cells  which  cover  and  conceal  it,  and  is  mounted  in  glycerine  with  or 
without  previous  staining  with  carmine. 

3.  Mount  in  Canada  balsam  sections  of  a  foetal  limb  which  has  been  stained 
with  magenta.     The  bones  will  be  found  in  different  stages  of  ossification, 
those  of  the  digits  being  least  developed.     Make  sketches  illustrating  the 
three  chief  stages  of  endochondral  ossification.      Notice  the   peculiar  ter- 
minal ossification  of  the  third  phalanx. 

4.  Make  with  a  sharp  scalpel  a  longitudinal  section  at  the  line  of  ossifica- 
tion in  a  more  advanced  bone  which  has  not  been  decalcified.     Other  sections 
may  be  carried  across  a  bone  near  its  plane  of  ossification,  and  others  through 
an  epiphysis.    These  sections  will  show  the  mode  of  progress  of  the  calcification. 
The  sections  can  be  mounted  in  glycerine. 


True  bone  is  essentially  formed  in  all  cases  by  an  ossification  of 
connective  tissue.  Sometimes  the  bone  is  preceded  by  cartilage,  which 
first  becomes  calcified,  and  this  is  then  invaded,  and  for  the  most  part 
removed,  by  an  embryonic  tissue  which  re-deposits  bony  matter  in 
the  interior  of  the  cartilage,  whilst  at  the  same  time  layers  of  bone  are 
being  formed  outside  underneath  the  periosteum.  This  is  intracar- 
tilaginous  or .  endochondral  ossification.  Sometimes  the  bone  is  not  pre- 
ceded by  cartilage,  and  then  the  only  process  which  occurs  is  one 
corresponding  to  the  subperiosteal  ossification  of  the  former  variety ; 
the  ossification  is  then  known  as  intramembranous. 

Ossification  of  cartilage. — This  may  be  described  as  occurring  in 
three  stages.  In  the  first  stage  the  cells  in  the  middle  of  the  cartilage 
become  enlarged  and  arranged  in  rows  radiating  from  the  centre 

1  For  the  methods  of  staining  and  embedding  1  and  3,  see  Appendix,  '  Embedding 
in  Paraffin.' 


DEVELOPMENT  OF  BONE. 


65 


(fig.  73),  and  fine  granules  of  calcareous  matter  are  deposited  in  the 
matrix.  Simultaneously  with  this  the  osteoblasts  underneath  the 
periosteum  deposit  a  layer  or  layers  of  fibrous  lamellae  upon  the  surface 
of  the  cartilage,  and  these  lamellae  also  become  calcified  (fig.  73,  im). 
As  they  are  formed,  some  of  the  osteoblasts  (o)  are  included  between 
them  and  become  bone-corpuscles. 


FIG.  73.— SECTION  OF  PHALANGEAL  BONE  OF  HUMAN  FCETUS,  AT  THE  TIME  OF 
COMMENCING  OSSIFICATION.  (From  a  preparation  by  F.  A.  Dixey.)£(Magnified 
about  75  diameters.) 

The  cartilage-cells  in  the  centre  are  enlarged  and  separated  from  one  another  by  dark-looking 
calcified  matrix ;  im,  layer  of  bone  deposited  underneath  the  periosteum  ;  o,  layer  of 
osteoblasts  by  which  this  layer  has  been  formed.  Some  of  the  osteoblasts  are  already  em- 
bedded in  the  new  bone  as  lacunae.  The  cartilage-cells  are  becoming  enlarged  and 
flattened  and  arranged  in  rows  above  and  below  the  calcified  centre.  At  the  ends  of  the 
cartilage  the  cells  are  small  and  the  groups  are  irregularly  arranged  ;  the  fibrous  perios- 
teum is  not  sharply  marked  off  from  the  cartilage. 

In  the  second  stage  some  of  the  subperiosteal  tissue  eats  its  way 'through 
the  newly  formed  layer  of  bone  and  into  the  centre  of  the  calcified  car- 


66 


THE  ESSENTIALS  OF  HISTOLOGY. 


tilage  (fig.  74,  ir).  This  is  freely  absorbed  before  it  (fig.  75),  so  that 
large  spaces  are  produced  which  are  filled  with  osteoblasts  and  contain 
numerous  blood-vessels  which  have  grown  in  at  the  same  time.  The 
spaces  are  termed  medullary  spaces,  and  this  second  stage  may  be 
termed  the  stage  of  irruption. 


irn 


FIG.  74. — SECTION  OF  PART  OF 

ONE  OF  THE  LIMB-BONES  OF 
A  FCETAL  CAT,  AT  A  MORE 
ADVANCED  STAGE  OF  OSSIFI- 
CATION THAN  IS  REPRESENTED 
IN  FIG.  73,  AND  SOMEWHAT 
MORE  HIGHLY  MAGNIFIED. 

(From  a  drawing  by  J.  Law- 
rence. ) 

The  calcification  of  the  cartilage- 
matrix  has  advanced  from  the 
centre,  and  is  extending  between 
the  groups  of  cartilage-cells  which 
are  arranged  in  characteristic 
rows.  The  subperiosteal  bony 
deposit  (im)  has  extended  pari 
passu  with  the  calcification  of  the 
cartilage-matrix.  The  cartilage- 
cells  in  the  primary  areolse  are 
mostly  shrunken  and  stellate  ;  in 
some  cases  they  have  dropped  out 
of  the  space.  At  ir  and  in  two 
other  places  an  irruption  of  the 
subperiosteal  tissue,  composed  of 
ramified  cells  with  osteoblasts 
and  growing  blood-vessels,  has 
penetrated  the  subperiosteal  bony 
crust,  and  has  begun  to  excavate 
the  secondary  areolje  or  medullary 
spaces ;  p,  fibrous  layer  of  the 
periosteum ;  o,  layer  of  osteo- 
blasts, some  of  them  are  embedded 
in  the  osseous  layer  as  bone- 
corpuscles  in  lacunae ;  bl,  blood- 
vessels occupied  by  blood-corpus- 
cles. Beyond  the  line  of  ossific 
advance  the  periosteum  may  be 
noticed  to  be  distinctly  incurved. 
This  incurvation  is  gradually 
moved  on,  the  cartilage  expand- 
ing behind  it  until  the  head  of  the 
bone  is  reached,  •  when  it  forms 
the  perioateal  notch  or  groove 
represented  in  fig.  77,  p.  69. 


In  the  third  stage  of  endochondral  ossification  there  is  a  gradual 
advance  of  the  ossification  towards  the  extremities  of  the  cartilage,  and 
at  the  same  time  a  gradual  deposition  of  fresh  bony  lamellae  and  spicules 
on  the  walls  of  the  medullary  spaces,  and  on  the  surface  of  the  new 
bone  under  the  periosteum.  The  advance  into  the  cartilage  always 
takes  place  by  a  repetition  of  the  same  changes,  the  cartilage-cells  first 
enlarging  and  becoming  arranged  in  rows,  the  matrix  between  the 


DEVELOPMENT  OF  BONE. 


67 


rows  becoming  calcified,  and  then  the  calcified  cartilage  becoming 
excavated  from  behind  by  the  osteoblastic  tissue  so  as  to  form  new 
medullary  spaces  (fig.  77).  The  walls  of  these  are  at  first  formed  only 
by  remains  of  the  calcified  cartilage-matrix  (fig.  77,  c),  but  they  soon 
become  thickened  by  lamellae  of  fibrous  bone  (b)  which  are  deposited 
by  the  osteoblasts,  and  between  which  bone-corpuscles  become  included, 


FIG.  75. — LONGITUDINAL  SECTION  THROUGH  PART  OF  A  PHALANX  OF  A  six  MONTHS 
HUMAN  EMBRYO.     (Kolliker.) 

The  calcified  cartilage  is  completely  absorbed  almost  to  the  limit  of  advancing  calcification. 
The  darker  substance  on  either  side  is  periosteal  bone.  The  embryonic  marrow  has  shrunk 
somewhat  away  from  it. 

as  in  the  case  of  the  subperiosteal  bone.  The  latter  advances  paripassu 
with  the  endochondral  calcification,  but  beyond  this  the  uncalcified 
cartilage  grows  both  in  length  and  breadth,  so  that  the  ossification  is 
always  advancing  into  larger  portions  of  cartilage ;  hence  the  endo- 
chondral bone  as  it  forms  assumes  the  shape  of  an  hour-glass,  the 
cylindrical  shape  of  the  whole  bone  being  maintained  by  additions  of 
periosteal  bone  to  the  outside  (see  fig.  76).  The  absorption  of  the 
calcified  cartilage-matrix  appears  to  be  effected,  as  is  the  case  with 


68 


THE  ESSENTIALS  OF  HISTOLOGY. 


absorption  of  bony  matter  wherever  it  occurs,  by  large  multi-nucleated 
cells  (fig.  77,  /,  /)  which  are  termed  osteoclaxts.     They  are  cells  of  the 


FIG.  76. — LONGITUDINAL  SEC- 
TION THROUGH  THE  UPPER 
HALF  OF  THE  DECALCIFIED 
HUMERUS  OF  A  FCETAL  SHEEP, 
AS  SEEN  UNDER  A  MAGNIFYING 
POWER  OF  ABOUT  30  DIA- 
METERS. (From  a  drawing  by 
J.  Lawrence.) 

ic,  the  part  of  the  shaft  which  was 
primarily  ossified  in  cartilage ; 
what  remains  of  the  primary  bone 
is  represented  as  dark,  enveloped 
by  the  clear  secondary  deposit. 
The  areola;  of  the  bone  are  occu- 
pied by  embryonic  marrow  with 
psteoblasts,  and  blood-vessels  var- 
iously cut,  represented  as  dark 
lines.  One  long  straight  vessel 
(bv)  passes  in  advance  of  the  line 
of  ossification  far  into  the  cartila- 
ginous head,  most  of  the  others 
loop  round  close  to  the  cartilage. 
At  one  or  two  places  in  the  older 
parts  of  the  bone  elongated  groups 
of  cartilage-cells  (c)  may  still  be 
seen,  which  have  escaped  absorp- 
tion. i«i,  the  part  of  the  bone 
that  has  been  ossified  in  mem- 
brane, that  is  to  say,  in  the  osteo- 
blastic  tissue  under  the  perios- 
teum. It  is  well  marked  off  from 
the  central  portion,  and  is  bound- 
ed, peripherally,  by  a  jagged  edge, 
the  projections  of  which  are  in- 
distinctly seen  to  be  prolonged  by 
bunches  of  osteogenic  fibres.  A 
row  of  osteoblasts  covers  the 
superficial  layer  of  the  bone.  The 
subperiosteal  layer  is  prolonged 
above  into  the  thickening  (p), 
which  encroaches  upon  the  carti- 
lage of  the  head  of  the  bone,  and 
in  which  are  seen,  amongst  nume- 
rous osteoblasts  and  a  few  blood- 
vessels, the  straight  longitudinal 
osteogenic  fibres  (of),  and  some 
other  fibres  (pf)  crossing  them, 
and  perhaps  representing  fibres 
of  Sharpey.  The  calcareous  salts 
having  been  removed  by  an  acid, 
the  granular  ossific  deposit  pass- 
ing up  between  the  rows  of  carti- 
lage-cells is  not  seen  in  this  speci- 
men ;  it  would  have  extended  as 
far  as  a  line  joining  the  marks 
x  x .  Observe  the  general  ten- 
dency of  the  osseous  trabeculge 
and  the  vascular  channels  between 
them  to  radiate  from  the  original 
centre  of  ossification.  This  is 
found  to  prevail  more  or  less  in 
all  bones  when  they  are  first 
formed,  although  the  direction  of 
the  trabeculae  may  afterwards  be- 
come modified  in  relation  with 
varying  physiological  conditions, 
and  especially  as  the  result  of 
pressure  in  different  directions. 


same  nature  as  the  myeloplaxes  of  the  marrow,  and  are  as  characteristic 
of  absorption  surfaces  as  are  the  osteoblasts  of  surfaces  where  bony 
deposit  is  proceeding  (fig.  78). 


DEVELOPMENT  OF  BONE. 


69 


The  bone  which  is  first  formed  is  more  reticular  and  less  regularly 
lamellar  than  that  of  the  adult,  and  contains  no  Haversian  systems. 
The  regular  lamella?  are  not  deposited  until  some  little  time  after 
birth,  and  their  deposition  is  generally  preceded  by  a  considerable 
amount  of  absorption.  It  is  about  this  time  also  that  the  medullary. 


FIG.  77. — PAKT  OF  A  LONGI- 
TUDINAL SECTION  OF  THE 
DEVELOPING  FEMUR  OF  THE 

BABBIT.  (Klein.)  (Drawn  un- 
der a  magnifying  power  of  350 
diameters. ) 

<i,  rows  of  flattened  cartilage-cells  : 
b,  greatly  enlarged  cartilage- 
cells  close  to  the  advancing  bone, 
the  matrix  between  is  partly 
calcified ;  c,  d,  already  formed 
bone,  the  osseous  trabeculaj 
being  covered  with  osteoblasts 
(e),  except  here  and  there, 
where  an  osteoclast  (/)  is  seen, 
eroding  parts  of  the  tuberculae ; 
g,  h,  cartilage-cells  which  have 
become  shrunken  and  irregular 
in  shape.  From  the  middle  of 
the  figure  downwards  the  dark 
trabeculaa,  which  are  formed  of 
calcified  cartilage-matrix,  are  be- 
coming covered  with  secondary 
osseous  substance  deposited  by 
the  osteoblasts.  The  vascular 
loops  at  the  extreme  limit  of  the 
bone  are  well  shown,  as  well  as 
the  abrupt  disappearance  of  the 
cartilage-cells. 


canal  of  the  long  bones  is  formed  by  the  absorption  of  the  bony  tissue 
which  originally  occupies  the  centre  of  the  shaft. 

After  a  time  the  cartilage  in  one  or  both  ends  of  the  long  bones  begins 
to  ossify  independently,  and  the  cpipliyses  are  formed.  These  are  not 
joined  to  the  shaft  until  the  growth  of  the  bone  is  completed.  Growth 
takes  place  in  length  by  an  expansion  of  the  cartilage  (intermediate  carti- 
lage} which  intervenes  between  the  shaft  and  the  epiphyses,  and  by  the 
gradual  extension  of  the  ossification  into  it ;  in  width  entirely  by  the 
deposition  of  fresh  bony  layers  under  the  periosteum.  In  the  terminal 


70 


THE  ESSENTIALS  OF  HISTOLOGY. 


phalanges  of  the  digits  the  ossification  starts,  not  from  the  middle  of 
the  cartilage,  but  from  its  distal  extremity. 

For  the  regeneration  of  portions  of  bone  which  have  been  removed 
by  disease  or  operation  it  is  important  that  the  periosteum  be  left. 

Intramembranous  ossification. — In  this  variety  of  ossification,  the 
bone  is  not  preceded  by  cartilage  at  all,  and  therefore  no  endochon- 
dral  bone  is  formed,  but  the  calcification  occurs  in  a  sort  of  embryonic 
fibrous  tissue  which  contains  numerous  osteoblasts  and  blood-vessels 
(fig.  79).  The  fibres  of  this  tissue  (osteogenic  fibres),  which,  like  those 
of  fibrous  tissue,  are  collected  into  small  bundles,  become  inclosed  in 
a  calcareous  matrix ;  and  as  the  fibres  grow,  the  calcification  extends 
further  and  further,  so  that  bony  spicules  are  formed,  which,  as  they 
become  thickened,  run  together  to  form  reticular  layers,  leaving  spaces 
filled  with  osteoblasts  around  the  blood-vessels.  The  osteogenic  fibres 
are  covered  with  osteoblasts,  and  as  the  bone  forms,  some  of  these 
become  left  as  bone-corpuscles  within  lacunae.  Thus  in  every  particular 


FIG.  78. — BONY  TRABECUL^E  FROM  THE  DEVELOPING  LOWER  JAW  or  A  CALF,  SHOWING 

OSTEOCLASTS   AT   THE    EXTREMITIES   WHERE    ABSORPTION    IS    PROCEEDING,    AND 
OSTEOBLASTS  COVERING  THE  SIDES  WHERE  DEPOSITION  OF  BONE  IS  GOING  ON. 

the  development  of.  these  bones  resembles  that  of  the  subperiosteal 
layer  of  endochondral  bone ;  which  is  also  to  be  considered  as  an  instance 
of  intramembranous  ossification,  although  taking  place  on  the  surface 
of  cartilage.  Moreover,  it  is  the  same  subperiosteal  tissue  which 
deposits  the  true  or  secondary  bone  upon  those  parts  of  the  calcified 
cartilage-matrix  which  have  escaped  absorption;  and  this  must  also, 
therefore,  be  reckoned  as  developed  according  to  the  same  type.  In 
fact,  even  in  intracartilaginous  ossification,  very  little  of  the  calcified 
cartilage-matrix  eventually  remains  ;  this  being  almost  wholly  absorbed 


DEVELOPMENT  OF  BONE. 


71 


and  either  replaced  by  true  or  fibrous  bone  which  has  been  formed  by 
osteoblasts,  or  swept  away  to  form  the  medullary  cavities. 


sp 


FIG.  79.— PART  OF  THE  GROWING  EDGE  OF  THE  DEVELOPING  PARIETAL  BONEjOP  A 
FOETAL  CAT,  1J  INCH  LONG.      (From  a  drawing  by  Mr.  J.  Lawrence.) 

sp,  bony  spicules,  with  some  of  the  osteoblasts  embedded  in  them,  producing  the  lacunae  ;  of, 
osteogenic  fibres  prolonging  the  spicules,  with  osteoblasts  (ost)  between  them  and  applied 
to  them. 


72  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  XV. 


STRUCTURE  OF  STRIATED  MUSCLE. 

1.  TAKE  a  shred  of  muscle  from  a  recently  killed  mammal,  and  on  a  dry  slide 
-carefully  separate  long  pieces  of  muscular  fibre  (single  fibres  if  possible)  and 
stretch  them  out,  keeping  them  moist  during  the  process  by  breathing  on  the 
slide.  Put  a  drop  of  serum  on  the  cover-glass  before  placing  this  over  the 
preparation.  Study  first  with  a  low,  then  with  a  high  power.  Sketch  all  the 
appearances  to  be  seen  in  a  small  piece  of  a  fibre,  focussing  carefully  the  most 
superficial  layers.  Notice  the  oval  nuclei  immediately  under  the  sarcolemma. 
Then  allow  a  little  dilute  acetic  acid  to  run  under  the  cover-glass  and  watch 
its  effect. 

2.  Prepare  some  fibres  of  frog's  muscle  in  the  same  way,  but  mount  in 
salt-solution  instead  of  serum.     Notice  the  muscular  substance   shrinking 
away  here  and  there  from  the  sarcolemma,  which  then  becomes  distinctly 
visible.     Sketch  a  piece  of  sarcolemma  bridging  across  an  interval  thus  pro- 
duced. 

3.  Study  transverse  sections  of  muscle  which  has  been  hardened  in  alcohol 
and  stained  with  hsematoxylin.     Mount  in  Canada  balsam.     Examine  first 
with  a  low  and  then  with  a  high  power.     Sketch  the  appearances  which 
are  seen. 

In   each   of   the   above    preparations   measure   the   diameter   of   some  of 
the  fibres. 

4.  Place  in  1  per  cent,  osmic  acid  a  small  shred  of  mammalian  muscular 
tissue  which  has  been  stretched  upon  a  cork.     After  24  hours,  when  it  will  be 
deeply  stained,  wash  it  in  water  and  with  needles  break  the  fibres  up  in 
glycerine  as  finely  as  possible.     Cover  and  examine  with  a  high  power. 


Voluntary  muscle  is  composed  of  long  cylindrical  fibres,  measuring 
on  an  average  about  ^J^  inch  in  diameter  in  mammalian  muscles,  but 
having  a  length  of  an  inch  or  more.  Each  fibre  has  an  elastic  sheath, 
the  sarcolemma,  which  incloses  the  contractile  substance.  The  sarco- 
lemma is  seldom  distinct,  unless  the  contained  substance  becomes 
broken  (fig.  80). 

The  contractile  substance  of  the  fibre  is  characterised  by  the  alter- 
nate dark  and  light  stripes  which  run  across  the  length  of  the  fibre ; 
hence  the  name,  cross-striated  or  striped  muscle.  On  focussing,  it  can  be 
seen  that  the  stripes  pass  through  the  whole  thickness  of  the  fibre ; 
they  may  therefore  be  looked  upon  as  representing  alternate  disks  of 
dark  and  light  substance.  If  the  surface  be  very  carefully  focussed, 


STRUCTURE  OF  STEIATED  MUSCLE. 


73 


rows  of  apparent  granules  are  seen  lying  in  or  at  the  boundaries  of  the 
light  streaks,  and  very  fine  longitudinal  lines  may,  with  a  good  micro- 
scope, be  detected  uniting  the  apparent  granules  (fig.  81).  These  fine 
lines,  with  their  enlarged  extremities  the  granules,,  are  more  conspicuous 
in  the  muscles  of  insects.  They  indicate  the  divisions  between  the 
longitudinal  elements  (muscle-columns,  sarcostyles)  which  compose 
the  fibre,  and  in  preparations  treated  with  dilute  acid  they  appear  to 
form  part  of  a  fine  network,  which  pervades  that  substance,  and  serves 
to  unite  the  granules  both  transversely  and  longitudinally.  This  net- 
work, which  is  sometimes  very  distinct  in  preparations  of  muscle 
treated  with  chloride  of  gold,  is,  hoAvever,  a  network  in  appearance 


FIG.  80. — SARCOLEMMA  OP  MAM- 
MALIAN MUSCLE,  HIGHLY  MAG- 
NIFIED. 

The  fibre  is  represented  at  a  place 
where  the  muscular  substance  has 
become  ruptured  and  has  shrunk 
away,  leaving  the  sarcolemma 
(with  a  nucleus  adhering  to  it) 
clear.  The  fibre  had  been  treated 
with  serum  acidulated  with  acetic 
acid. 


FIG.  81.— MUSCULAR  FIBRE  OF  A 
MAMMAL  EXAMINED  FRESH  IN 

SERUM,  HIGHLY  MAGNIFIED, 
THE  SURFACE  OF  THE  FIBRE 
BEING  ACCURATELY  FOCUSSED. 
The  nuclei  are  seen  on  the  flat  at  the 
surface  of  the  fibre,  and  in  profile 
at  the  edges. 


only  :  in  reality  it  is  the  optical  expression  of  the  interstitial  substance 
which  lies  between  the  muscle-columns.  This  substance  is  termed 
sarcoplasm. 

A  fine  clear  line  is  sometimes  seen  running  transversely  across  the 
fibre  in  the  middle  of  each  dark  band.  This  is  termed  Hensen's  line. 

On  examining  the  transverse  section  of  a  fibre  with  a  high  power,  it 
is  seen  to  be  subdivided  everywhere  into  small  angular  fields,  the  areas 
of  Cohnheim.  These  represent  sections  of  the  sarcostyles  of  which  the 
fibres  are  composed,  and  into  which  they  may  be  split  after  death,  or 
after  being  hardened  in  certain  reagents,  e.g.  chromic  acid  or  osmic 
acid. 


74 


THE  ESSENTIALS  OF  HISTOLOGY. 


FIG.  82.— PORTION  OF  A  MEDIUM - 

SIZED  HUMAN  MUSCULAR  FIBRE, 
SHOWING  THE  INTERMEDIATE 
LINE  MENTIONED  IN  THE  TEXT. 

(Sharpey.) 


If  instead  of  focussing  the  surface  of 
the  fibre  it  be  observed  in  its  depth, 
an  appearance  different  from  that 
shown  in  fig.  81  is  frequently  visible, 
namely,  a  fine  dotted  line  bisecting 
each  clear  stripe  (fig.  82) ;  this  ap- 
pearance is  often  considered  to  re- 
present a  membrane  (Krausds  mem- 
brane), which  subdivides  the  sarco- 
styles  at  regular  intervals  (see  p.  77). 
But  Krause's  membrane  is  rarely,  if 
ever,  visible  in  fresh  muscle,  and  it  is 
much  more  probable  that  the  line  in 
question  is  an  interference  line,  caused 
by  the  light  being  transmitted  between 
disks  of  different  refrangibility.  Hay- 
craft  believes  that  the  cross-striation 
of  voluntary  muscle  is  entirely  due  to 
refractive  effects  produced  by  a  vari- 
cosity  of  the  component  sarcostyles, 
but  in  view  of  the  entirely  different 
manner  in  which  the  substance  of  the 
dark  and  clear  stripes  behave  to  many 
staining  reagents,  and  especially  to 
chloride  of  gold  when  applied  as 
directed  in  Lesson  XVL,  sec.  3,  this 
position  must  be  regarded  as  unten- 
able. 

Besides  the  sarcolemma  and  striated  substance,  a  muscular  fibre  also 
exhibits   a   number   of   oval   nuclei   which   have   the  usual  structure 
of    cell-nuclei  :    the    chromoplasm    often    has    a   spiral   arrangement. 
Sometimes  there  is  a  little  granular  substance  (protoplasm)  at  each 
pole   of   the  nucleus,   and  the  nuclei   with   the   adjacent   protoplasm 
are  then  spoken  of  as  muscle-corpuscles.     In  mammalian   muscle   the 
nuclei  usually  lie  immediately  under  the  sarcolemma  (figs.  80,  81,  83), 
except  in  certain  fibres,  which  entirely  compose 
the  red  muscles  of  some  animals,  such  as  the 
rabbit,  and  which  occur  scattered  amongst  the 
ordinary  fibres  in  mammalia  generally.    In  these 
the  nuclei  are  distributed  through  the  thickness 
of  the  fibre,  and  this  is  also  the  case  in  all  the 
muscular  fibres  of  the  frog.     In  some  muscle- 
fibres,  such  as  those  of  the  diaphragm,  which 
FIG.  83.— SECTION  OF  A  MUS- 
CULAR FIBRE,  SHOWING  are  in  constant  activity,  the  protoplasm  of  the 
AREAS  OF  COHNHEIM.       muscie_c0rpuscles  is  often  greatly  developed. 
The  transverse  section  of  a  muscle  shows  the  fibres  to  be  nearly 
cylindrical  in  figure.     Between  the  fibres  there  is  a  certain  amount  of 
areolar  tissue,  which  serves  to  support  the  blood-vessels  and  also  unites 
them  into  fasciculi :  the  fasciculi  are  again  united  together  by  a  larger 
amount  of  this  intramuscular  connective  tissue  (endomysiuin). 


STRUCTURE  OF  STRIATED  MUSCLE.  75 


LESSON  XVI. 

STRUCTURE  OF  STRIATED  MUSCLE  (continued}. 

1.  CUT  off  the  head  of  a  beetle  or  other  large  insect  (e.g.  bee,  wasp),  and 
bisect  the  trunk  with  scissors  so  as  to  expose  the  interior.  Notice  two  kinds 
of  muscular  tissue,  the  one  belonging  to  the  legs  greyish  in  colour,  the  other 
attached  to  the  wings  yellowish.  Preparations  of  both  kinds  of  muscle  are 
to  be  made  in  the  same  way  as  living  mammalian  muscle  (see  previous 
Lesson),  but  it  is  better  to  mount  them  either  in  a  drop  of  white  of  egg  or  of 
the  insect's  blood.  In  both  preparations  the  dark-looking  air-tubes  or 
tracheae  form  prominent  objects  ramifying  amongst  the  fibres.  Observe  the 
structure  of  the  two  kinds  of  muscle  so  far  as  it  can  be  made  out  in  the  fresh 
preparation.  If  the  preparation  is  made  quickly,  waves  of  contraction  will 
probably  be  observed  passing  along  the  fibres. 

2.  Make  another  preparation,  mounting  the  muscle  in  vinegar.     (Alcohol- 
hardened  muscle  may  be  used  for  this  purpose.)     Notice  that  the  muscular 
substance  swells  up  somewhat  and  becomes  clearer,  whilst  the  sarcoplasm-net- 
work  of  the  leg  muscles,  with  its  lines  and  dots,  comes  more  distinctly  into 
view.    In  a  well-teased  preparation  of  alcohol-hardened  muscle,  the  leg-fibres 
will  be  frequently  found  breaking  across  into  disks.     Make  careful  drawings 
from  this  preparation. 

3.  Place  an  insect  (wasp,  beetle)  into  90  per  cent,  alcohol  for  24  or  48  hours. 
Then  take  a  small  piece  of  each  kind  of  muscle,  and  place  in  strong  glycerine 
for  some  hours  to  remove  the  alcohol.     Transfer  to  1  per  cent,  chlo'ride  of 
gold  solution  :  leave  the  pieces  of  muscle  in  this  from  15  to  30  minutes 
according  to  their   size.     From  the  gold  solution  they  are  transferred  to 
formic  acid  (1  part  of  the  strong  acid  to  3  of  water),  and  kept  in  the  dark  for 
•24  hours,  but  they  may  be  kept  longer  without  disadvantage.     The  muscle  is 
then  teased  in  glycerine.     Some  of  the  fibres  will  be  found  after  this  method 
to  have  their  sarcoplasm  darkly  stained,  and  to  show,  therefore,  the  appear- 
ance of  a  network  both  in  longitudinal  and  transverse  view  :  others,  on  the 
other  hand,  have  the  sarcous  elements  stained,  and  the  sarcostyles  are  thereby 
rendered  very  evident,  but  the  sarcoplasm  is  unstained.     Some  fibres  may 
show  an  intermediate  condition. 


Ordinary  or  leg-muscles  of  insects. — In  the  muscles  of  insects  the 
stripes  are  relatively  broad,  and  their  structure  can  be  more  readily 
seen  than  in  mammals.  In  the  living  fibres  from  the  muscles  of  the 
legs,  the  sarcoplasm  presents  a  striking  appearance  of  fine  longitudinal 
lines  traversing  the  muscle,  and  enlarging  within  the  light  stripes  into 
rows  of  dots.  This  is  still  better  seen  in  fibres  and  portions  of  fibres 
which  have  been  treated  with  dilute  acid.  In  separated  disks  produced 


THE  ESSENTIALS  OF  HISTOLOGY. 


by  the  breaking  across  of  muscle-fibres,  the  surfaces  of  the  disks  show  a 
network  with   polyhedral  meshes  in  some  insects,  one  formed  of  lines 


FlG.  85. — POKTION  OP  LEG-MUSCLE 
OF  INSECT  TREATED  WITH  DILUTE 
ACID. 

S,  sarcolemma ;   D,   dot-like   enlarge- 
ment of  sarcoplasm  ;    K,  Krause's 
membrane.     The  sarcous  elements 
FIG.  84. — LIVING  MUSCLE  OF  WATER-BEETLE  (DY-        are  swollen  and  dissolved  by  the 

TISCUS  MARGINALIS).      (Highly  magnified. )  action  of  the  acid. 

s,  sarcolemma  ;  a,  dim  stripe  ;  6,  bright  stripe  ;  c,  row  of 
dots  in  bright  stripe,  which  seem  to  be  the  enlarged 
ends  of  rod-shaped  particles,  d,  but  are  really  expan- 
sions of  the  interstitial  sarcoplasm. 

radiating  from  the  centre  of  the  fibre  in  others.     The  nuclei,  with  some 
inclosing  protoplasm,  usually  lie  in  the  middle  of  the  fibre. 


FIG.  86. — TRANSVERSE  SECTIONS  OF  INSECT  LEG-MUSCLE,  VIEWED  IN  ISOLATED  DISKS, 

TREATED  WITH  DILUTE  ACID. 

A,  from  a  beetle.     The  disk  is  viewed  partly  on  the  flat,  partly  in  profile  ;  the  sarcoplasm 

appears  longitudinally  as  lines,  transversely  as  a  network. 

B,  from  a  wasp,  showing  a  radial  disposition  of  the  sarcoplasm. 

Wing- muscles  of  insects. — The  wing-muscles  of  insects  are  easily 
broken  up  into  sarcostyles,  which  also  show  alternate  dark  and  light 
strise. 

The  sarcostyles  are  subdivided  at  regular  intervals  by  transverse 
membranes  into  successive  portions,  which  may  be  termed  sarcomeres. 
Each  sarcomere  is  occupied  by  a  portion  of  the  dark  stria  of  the  whole 
fibre  (sarcous  element) :  the  sarcous  element  is  really  double,  and  in  the 
stretched  fibre  separates  into  two  at  the  line  of  Hensen  (figs.  87,  D ; 


STKUCTUKE  OF  STEIATED  MUSCLE. 


77 


88,  B).  At  either  end  of  the  sarcous  element  is  a  clear  interval  separat- 
ing it  from  the  membrane  of  Krause  :  this  clear  interval  is  more  evident 
the  more  the  sarcostyle  is  extended,  but  diminishes  to  complete  dis- 
appearance in  the  contracted  muscle  (figs.  87,  88,  A).  The  cause  of  this 


FIG.  87. — FIBRES  OF  THE  WING- 
MUSCLES  OP  AN  INSECT. 
(Ranvier. ) 

The  fibres  are  in  different  conditions 
of  extension,  from  A  least  ex- 
tended, to  D  most  extended,  e,  e, 
sarcous  elements  ;  m,  m,  mem- 
branes of  Krause ;  be,  clear  inter- 
vals on  either  side  of  Krause's 
membranes,  which  in  the  stretched 
sarcostyles  are  occupied  by  fluid 
which  has  passed  out  from  the 
pores  of  the  sarcous  elements  ;  h, 
separation  of  the  sarcous  element 
into  two  parts,  a  clear  interval 
being  left  between  them. 


is  to  be  found  in  the  structure  of  the  sarcous  element.  Each  sarcous  ele- 
ment is  pervaded  with  longitudinal  canals  or  pores,  which  are  open  in 
the  direction  of  Krause's  membranes,  but  closed  at  the  middle  of  the 
sarcous  element.  In  the  contracted  or  retracted  muscle,  the  clear  part  of 


A' 


FIG.  88. — SARCOSTYLES  or  THE  WINO- 

MUSCLES  OP  A  WASP,  PREPARED   IN 
THE  MANNER  DESCRIBED  IN  LESSON 

xvi.,  SEC.  3.    (Highly  magnified.) 

A,  A',  sarcostyles  showing  degrees  of 
contraction.  B,  an  extended  sarco- 
style, with  its  sarcous  elements  separ- 
ated at  the  line  of  Hensen.  C,  three 
sarcostyles  moderately  extended.  The 
structure  of  the  sarcous  elements, is 
shown  diagrammatically. 


the  muscle-substance  has  passed  into  these  pores,  and  therefore  disappeared 
from  view,  but  swells  up  the  sarcous  element  and  shortens  the  sarcomere  : 
in  the  extended  muscle,  on  the  other  hand,  the  clear  part  has  passed  out 
from  the  pores  of  the  sarcous  element,  and  now  lies  between  this  and  the 


78 


THE  ESSENTIALS  OF  HISTOLOGY. 


membrane  of  Krause,  the  sarcomere  being  thereby  lengthened  and 
narrowed.  The  sarcous  element  does  not  lie  free  in  the  middle  of  the 
sarcomere,  but  is  attached  laterally  to  a  fine  inclosing  envelope,  and  at 
either  end  to  Krause's  membrane  by  very  fine  lines,  which  may  repre- 
sent fine  septa,  running  through  the  clear  substance  (fig.  90). 


FIG.  89. — AN  ISOLATED  SARCOUS  ELEMENT 
OF  A  WING -MUSCLE,  SHOWING  ITS  TUBU- 
LAR OR  POROUS  STRUCTURE.  (Magnified 
2300  diameters.) 

A,  profile  view ;  B,  surface  view,  seen  on 
the  flat. 


FIG.  90.— DIAGRAM  or  A  SARCOMERE  IN  A 

MODERATELY    EXTENDED    CONDITION   A, 
AND  IN  A  CONTRACTED  CONDITION  B. 

K,  K,  membranes  of  Krause  ;  H,  line  or  plane 
of  Hensen  ;  S.  E. ,  poriferous  sarcous  element. 


If  we  compare  the  structure  of  the  sarcomere  with  that  of  the  protoplasm 
of  an  amoeboid  cell  we  find  several  points  in  common.  In  both  there  is  a 
framework  of  labile  material  (spongioplasm,  substance  of  sarcous  element), 
which  tends  to  stain  with  hsematoxylin  arid  similar  reagents,  and  which 
incloses  in  its  meshes  or  pores  a  clear,  probably  semi-fluid  substance  (hyalo- 
plasm, clear  substance  of  sarcomere),  which  remains  unstained  by  these 
reagents.  In  both  instances  also  the  clear  substance  or  hyaloplasm,  when 
the  tissue  is  subjected  to  stimulation,  passes  into  the  pores  of  the  porous  sub- 
stance or  spongioplasm  (contraction),  whilst  in  the  absence  of  such  stimula- 
tion it  tends  to  pass  out  from  the  spongioplasm  (formation  of  pseudopodia, 
extension  of  muscle).  Thus  both  the  movements  of  cell-protoplasm  and 
those  of  muscle  may  be  described  as  being  brought  about  by  similar  means, 
although  at  first  sight  the  structure  of  muscle  is  so  dissimilar  from  that  of 
protoplasm.  We  have  already  noticed  that  the  movements  of  cilia  are 
susceptible  of  a  similar  explanation  (p.  36). 


STRUCTURE  OF  MUSCLE.  79 


LESSON  XVII. 

CONNECTION  OF  MUSCLE  WITH  TENDON;  BLOOD-  VESSELS  OF 
MUSCLE;  CARDIAC  MUSCULAR  TISSUE;  DEVELOPMENT  OF 
MUSCLE;  PLAIN  MUSCULAR  TISSUE. 

1.  To  study  the  connection  of  muscle  with  tendon,  a  frog  is  killed  by  de- 
struction of  the  brain  and  spinal  cord,  and  placed  in  about  a  litre  of  water  raised 
to  a  temperature  of  55°  C.  It  is  left  in  this  for  15  minutes,  the  water 
gradually  cooling.  It  is  then  easy  to  dissociate  the  muscular  fibres  in  large 
numbers.  To  observe  their  attachment  to  the  tendon-bundles  a  fine  longi- 
tudinal shred  must  be  snipped  off  with  scissors  at  the  tendinous  attachment, 
and  dissociated  upon  a  slide  in  a  drop  of  water.  It  will  usually  be  found 
that  the  muscular  substance  is  retracted  from  the  end  of  the  sarcolemma 
tube,  which  is  firmly  cemented  to  the  tendon  bundle.  The  structure  may  be 
brought  more  distinctly  into  view  by  adding  to  the  dissociated  fibres  a  drop 
of  a  weak  solution  of  iodine  in  salt-solution  or  in  serum  (iodised  serum).1 
To  preserve  the  specimen,  mount  it  in  dilute  glycerine  coloured  by  magenta. 

2.  The  blood-vessels  of  muscle.     These  are  to  be  studied  in  longitudinal 
and  transverse  sections  of  injected  muscle.     It  will  be  noticed  that  the  capil- 
laries are  very  numerous,  and  form  a  network  with  oblong  meshes.     In  the 
red  muscles  of  the  rabbit,  small  dilatations  are  seen  on  the  transverse  cords 
of  the  network. 

3.  The  muscular  tissue  of  the  heart  is  studied  in  sections  of  that  organ 
arid  also  in  teased  preparations.     To  prepare  the  latter,  place  a  small  piece 
of  heart-muscle  in  30  per  cent,  alcohol  for  a  few  days  :  stain  in  picro-carmine 
solution  (see  Appendix)  for  some  hours  ;  and  tease  in  dilute  glycerine. 

4.  Tear  off  a  small  shred  of  the  muscular  coat  of  a  piece  of  intestine  which 
has  been  from  24  to  48  hours  in  £  per  cent,  bichromate  of  potash  solution. 
Hold  the  shred  with  forceps  in  a  drop  of  water  and  fray  it  out  with  a  needle. 
In  this  process  many  cells  will  be  set  free  and  can  be  seen  with  a  low  power. 
The  preparation  may  then  be  covered  and  examined  with  a  high  power. 
Sketch  one  of  the  cells.     Then  allow  hsematoxylin  solution  to  pass  under  the 
cover-glass  and  lastly  a  drop  of  glycerine.     Sketch  another  cell  after  staining. 
Measure  two  or  three  cells  and  their  nuclei. 

Ending  of  muscle  in  tendon. — A  small  tendon-bundle  passes  to 
each  muscular  fibre  and  becomes  firmly  united  with  the  sarcolemma, 
which  extends  over  the  end  of  the  fibre  (fig.  91).  Besides  this  immed- 
iate attachment,  a  further  connection  is  established  by  the  fact  that 
the  areolar  tissue  between  the  tendon-bundles  is  continuous  with  that 
which  lies  between  the  muscular  fibres. 

1  This  method  is  the  one  given  by  Kanvier  (Traite  Technique,  2me  edition,  p.  395). 
The  muscle-endings  may  also  sometimes  be  well  seen  at  the  extremities  of  the  tendons, 
which  are  removed  from  the  mouse's  tail  in  the  manner  described  in  Lesson  X.,  p.  45. 


80 


THE  ESSENTIALS  OF  HISTOLOGY. 


Blood-vessels  of  muscle. — The  capillaries  of  the  muscular  tissue  are 
very  numerous.  They  run,  for  the  most  part,  longitudinally,  with 
transverse  branches,  so  as  to  form  long  oblong  meshes  (fig.  92).  In 
the  red  muscles  of  the  rabbit,  the  transverse  capillaries  have  small 
dilatations  upon  them.  No  blood-vessels  ever  penetrate  the  sarco- 
lemma. 


FIG.  91. — TERMINATION  OF  A  MUS- 
CULAR FIBRE  IN  TENDON.  (Ran- 
vier.) 

T»,  sarcolemma;  *,  the  same  membrane  FlG-    92.— CAPILLARY    VESSELS    OF 

passing  over  the  end  of  the  fibre  ;  p,  MUSCLE, 

extremity  of  muscular  substance,  c, 
retracted  from  the  lower  end  of  the 
sarcolemma-tube ;  t,  tendon-bundle 
passing  to  be  fixed  to  the  sarcolemma. 

Lymphatic  vessels,  although  present  in  the  connective-tissue  sheath 
(perimysium)  of  a  muscle,  do  not  penetrate  between  its  component  fibres. 

The  nerves  of  voluntary  muscles  pierce  the  sarcolemma  and  terminate 
in  a  ramified  expansion  known  as  an  end-plate  (See  Lesson  XX.). 

Development. — Voluntary  muscular  fibres  are  developed  from  em- 
bryonic cells  of  the  mesoderm,  which  become  elongated,  and  the  nuclei 
of  which  become  multiplied,  so  as  to  produce  long  multi-nucleated 
fusiform  or  cylindrical  fibres.  These  become  cross-striated  at  first 
along  one  side,  the  change  gradually  extending  around  the  fibre  and 


STKUCTUBE  OF  MUSCLE. 


81 


also  towards  the  centre ;  but  the  middle  of  the 
nuclei  are  at  first  confined,  remains  for  some 
time  unaltered  (fig.  93).  Eventually  the  change 
in  structure  extends  to  this  also,  and  the  nuclei 
pass  gradually  to  occupy  their  ordinary  position 
under  the  sarcolemma,  which  by  this  time  has 
become  formed. 

The  muscular  substance  of  the  heart  (cardiac 
muscle)  is  composed  of  transversely  striated 
muscular  fibres,  which  differ  from  those  of 
voluntary  muscle  in  the  following  particulars  : 
their  striations  are  less  distinct ;  they  have  no 
sarcolemma ;  they  branch  and  unite  with  neigh- 
bouring fibres,  and  their  nuclei  lie  in  the  centre 
of  the  fibres.  Moreover,  the  fibres  are  com- 
posed of  a  series  of  short  cylindrical  cells  (figs. 
94,  95)  joined  together  end  to  end,  each  cor- 
responding to  one  of  the  nuclei.  The  lines  of 
junction  of  these  cells  may  sometimes  be  seen 
in  longitudinal  sections  stained  with  haema- 
toxylin  or  carmine ;  but  they  come  much  more 
distinctly  into  view  in  sections  of  the  fresh  tissue 
of  silver. 


K 


fibre,  to  which  the 


FIG.    93.— DEVELOPING 

MUSCULAR  FIBRE  PROM 
FCETUS   OF   2  MONTHS. 

(Ranvier.) 

p,  central  protoplasm  with 
several!  nuclei,  n,  scat- 
tered in  it ;  «,  commenc- 
ing sarcolemma,  with 
striated  muscular  sub- 
stance developing  imme- 
diately beneath  it. 

stained  with  nitrate 


FIG.  94.— MUSCULAR  FIBRES  FROM  THE 
HEART,  MAGNIFIED,  SHOWING  THEIR 
CROSS-STRLE,  DIVISIONS,  AND  JUNC- 
TIONS. (Schweigger-Seidel.) 

The  nuclei  and  cell -junctions  are  only  repre- 
sented on  the  right-hand  side  of  the  figure. 


FlG.      95.— SIX     MUSCULAR     FIBRE-CELLS 

FROM   THE    HEART.      (Magnified  425 
diameters.) 

a,  line  of  junction  between  two  cells ;  6,  c, 
branching  of  cells.  (From  a  drawing  by 
J.  E.  Neale.) 


THE  ESSENTIALS  OF  HISTOLOGY. 


Involuntary  or  plain  muscular  tissue  is  composed  of  long,  some- 
what flattened,  fusiform  cells  (fig.  96), 
which  vary  much  in  length,  but  are 
usually  not  more  than  ^^  inch  long. 
Each  cell  has  an  oval  or  rod-shaped 
nucleus,  which  shows  the  usual  intra- 
nuclear network  and  commonly  one  or 
two  nucleoli.  The  celL-substance  is 
longitudinally  striated,  but  does  not 
exhibit  cross-stria3  like  those  of  volun- 
tary muscle.  There  appears  to  be  a 
delicate  sheath  to  each  cell.  There  is 
a  little  intercellular  cementing  sub- 
stance uniting  the  cells  together,  which 
can  be  stained  by  nitrate  of  silver,  and 
this  intercellular  substance  is  bridged 
across  by  fine  filaments  passing  from 
cell  to  cell.  The  fibres  are  collected 
into  fasciculi. 

Plain  muscular  tissue  is  found  chiefly 
in  the  walls  of  hollow  viscera ;  thus  it 
forms  the  muscular  coat  of  the  whole 
of  the  alimentary  canal  below  the 
oasophagus,  and  occurs  abundantly  in 
the  muscular  coat  of  that  tube  also, 
although  it  is  here  intermixed  with 
cross-striated  muscle ;  it  is  found  also 
in  the  mucous  membrane  of  the  alimen- 
tary canal ;  in  the  trachea  and  its  rami- 
fications ;  in  the  urinary  bladder  and 
ureters  ;  in  the  uterus,  Fallopian  tubes, 
and  ovary ;  in  the  prostate,  the  spleen, 
and  muscle  of  Miiller  in  the  orbit,  and 
in  the  ciliary  muscle  and  iris.  The 
walls  of  gland-ducts  also  contain  it,  and 
the  middle  coat  of  the  arteries,  veins, 
and  lymphatics  is  largely  composed  of 
this  tissue.  It  occurs  also  in  the  skin, 
both  in  the  secreting  part  of  the  sweat- 
glands,  and  in  small  bundles  attached  to  the  hair-follicles;  in  the 
scrotum  it  is  found  abundantly  in  the  subcutaneous  tissue  (dartos),  and 
it  also  occurs  in  the  areola  of  the  nipple. 


FIG.     96. — MUSCULAR    FIBRE-CELLS 

FROM  THE  MUSCULAR  COAT  OF  THE 
SMALL  INTESTINE,  HIGHLY  MAG- 
NIFIED. 

A,  a  complete  cell,  showing  the  nucleus 
with  intra-nuclear  network,  and  the 
longitudinal  fibrillation  of  the  cell- 
substance,  with  finely  vacuolated 
protoplasm  between  the  fibrils ;  B,  a 
cell  broken  in  the  process  of  isolation  ; 
a  delicate  enveloping  membrane  pro- 
jects at  the  broken  end  a  little  beyond 
the  substance  of  the  cell. 


STRUCTURE  OF  NERVE-FIBRES.  83 


LESSON  XVIII. 

STRUCTURE  OF  NERVE-FIBRES. 

1.  TEASE  a  piece  of  fresh  nerve  in  saline  solution  (or  by  the  method  of 
demidesiccation,  afterwards  mounting  in  salt  solution),  injuring  the  fibres  as 
little  and  obtaining  them  as  long  and  straight  as  possible.  Study  the  medul- 
lated  fibres,  carefully  noticing  all  the  structures  that  are  visible — viz.,  nodes 
of  Ranvier,  nuclei  of  primitive  sheath,  double  contour  of  medullary  sheath, 
medullary  segments,  etc.  Measure  the  diameter  of  half  a  dozen  fibres.  Draw 
a  short  length  of  a  fibre  very  exactly. 

•2.  Prepare  a  piece  of  a  sympathetic  nerve  in  the  same  way.     Measure  and 
sketch  as  before. 

3.  Separate  (in  dilute  glycerine)  into  its  fibres  a  small  piece  of  nerve  or 
nerve-root  that  has  been  twenty-four  hours  in  \  per  cent,  osmic  acid.     The 
nerve  should  have  been  moderately  stretched  on  a  piece  of  cork  by  means  of 
glass  pins  before  being  placed  in  the  acid.     Keep  the  fibres  as  straight  as 
possible  and  only  touch  them  near  their  ends  with  the  needles.     Sketch  two 
portions  of  a  fibre  under  a  high  power,  one  showing  a  node  of  Ranvier  and 
the  other  a  nucleus  of  the  primitive  sheath.     Look  for  fibres  of  Remak. 
Measure  the  length  of  the  nerve-segments  between  the  nodes  of  Ranvier. 

4.  Mount  in  Canada  balsam  sections  of  a  nerve  which  has  been  hardened 
in  picric  acid.     Stain  with  picro-carmine  or  hsematoxylin.     The  nerve  should 
be  straitened  out  before  being  placed  in  the  hardening  solution.     Examine 
the  sections  first  with  a  low  and  afterwards  with  a  high  power.     Notice  the 
lamellar  structure  of  the  peririeurium,  the  varying  size  of  the  nerve-fibres, 
the  axis-cylinder  in  the  centre  of  each  fibre,  etc.     Measure  the  diameter  of 
five  or  six  fibres,  and  sketch  a  small  portion  of  one  of  the  sections. 


Nerve-fibres  are  of  two  kinds,  medullated  and  non-medullated.  The 
cerebro-spinal  nerves  and  the  white  matter  of  the  nerve-centres  are 
composed  of  medullated  fibres ;  the  sympathetic  and  its  branches  is 
chiefly  made  up  of  non-medullated. 

The  medullated  or  white  fibres  are  characterised,  as  their  name 
implies,  by  the  presence  of  the  so-called  medullary  sheath  or  white 
substance.  This  is  a  layer  of  soft  substance,  physically  of  a  fatty  nature, 
which  encircles  the  essential  part  of  a  nerve-fibre,  viz.,  the  axis-cylinder. 
Outside  the  medullary  sheath  is  a  delicate  but  tough  homogeneous 
membrane,  the  primitive  sheath  or  nucleated  sheath  of  Schwann,  but  this 
is  not  present  in  all  medullated  fibres,  being  absent  in  those  which  are 
within  the  nerve-centres.  The  primitive  sheath  is  also  known  as  the 
neurolemma. 


84 


THE  ESSENTIALS  OF  HISTOLOGY. 


The    medullary  sheath   is   composed    of    a    highly    refracting    fatty 
material,  which  gives  a  characteristic  dark  contour  and  tubular  appear- 


II 


FIG.  97. — WHITE  OR  MEDULLATED 
NERVE  -  FIBRES,    SHOWING    THE 

SINUOUS    OUTLINE    AND    DOUBLE 
CONTOURS. 


FIG.  98.— PORTIONS  OP  TWO  NERVE-FIBRES 
STAINED  WITH  OSMIC  ACID  (FROM  A 
YOUNG  RABBIT).  (425  diameters.) 

R,  a,  nodes  of  Ranvier,  with  axis-cylinder 
passing  through,  a,  primitive  sheath  of 
the  nerve ;  c,  opposite  the  middle  of  the 
segment,  indicates  the  nucleus  and  proto- 
plasm lying  between  the  primitive  sheath 
and  the  medullary  sheath.  In  A  the  nodes 
are  wider,  and  the  intersegmental  sub- 
stance more  apparent  than  in  B.  (Drawn 
by  J.  E.  Neale.) 


ance  to  the  nerve-fibres.  It  affords  a  continuous  investment  to  the- 
axis -cylinder,  except  that  it  is  interrupted  at  regular  intervals  in  the 
course  of  the  peripheral  nerve-fibres,  the  axis-cylinder  at  these  places 


STRUCTURE  OF  NERVE-FIBRES. 


85 


being  encompassed 
only  by  the  primi- 
tive sheath.  Hence 
the  primitive  sheath 
appears  at  these 
spots  to  produce  a 
constriction  in  the 
nerve-fibre,  and  the 
interruptions  of  the 
medullary  sheath  are 
accordingly  known 
as  the  constrictions  or 
mules  of  Banner  (fig. 
98,R,R;  fig.  100,  L), 
the  term  nodes  being 
.applied  from  the  re- 
semblance which  they  FlG.  99.— A  SMALL  PART  OF  A  MEDUL- 
LATED  FIBRE,  HIGHLY  MAGNIFIED. 

bear    to    the    nodes 

The  fibre  looks  in  optical  section  like  a  tube  — 
hence  the  term  tubular,  formerly  applied  to 


these  fibres.  .Two  partial  breaches  of  con- 
tinuity are  seen  in  the  medullary  sheath, 
which  at  these  places  exhibits  a  tendency  to 
split  into  laminae.  The  primitive  sheath  is 
here  and  there  apparent  outside  the  medul- 
lary sheath,  and  the  delicate  stria?  which 
ai-e  visible  in  the  middle  of  the  fibre  pro- 
bably indicate  the  fibrillated  axis-cylinder. 


of  a  bamboo.  The 
length  of  nerve  be- 
tween two  successive 
nodes  may  be  termed 
an  internode;  in  the 
middle  of  each  inter- 
node  is  one  of  the 
nuclei  of  Schwann's 
sheath.  Besides 
these  interruptions 
the  medullary  sheath 
shows  a  variable 
number  of  oblique 
clefts  (figs.  99,  100), 
which  subdivide  it 
into  irregular  por- 
tions, which  have 
been  termed  medul- 

lary     segments,      but  FIG.  101.  -Two  PORTIONS  OF  MEDULLATED 
there    is    reason     to        NERVE-FIBRES,     AFTER     TREATMENT 

WITH  OSMIC  ACID,  SHOWING  THE  AXIS- 

believe  that  the  clefts       CYLINDER,    AND     THE    MEDULLARY 

SHEATHS'    (Key  and 


are    artificially    pro- 

duced.        Osmic    acid    A,  node  of  Ranvier.     B,  middle  of  an  inter- 
c;tflinc  tViA  morliillayTr       node  with  nucleus.    c,  axis-cylinder,  pro- 
lliary        jecting  ;  p,  primitive  sheath,  within  which 
the  medullary  sheath,  which  is  stained  dark 
by  the  osmic  acid,  is  somewhat  retracted. 


FIG.  100.— NERVE- 
FIBRE  STAINED 
WITH  OSMIC  ACID. 

(Key&Retzius.) 


86 


THE  ESSENTIALS  OF  HISTOLOGY. 


The  axis-cijliiider,  which  runs  along  the  middle  of  the  nerve-fibre, 
is  a  soft  transparent  thread  which  is  continuous  from  end  to  end  of 
the  nerve.1 


FIG.    102. — AXIS-CYLINDER, 

HIGHLY  MAGNIFIED,  SHOW- 
ING THE  FIBRILS  COMPOS- 
ING IT.  (M.  Schultze.) 


FIG.  103.— SECTION  ACROSS  FIVE 
NERVE-FIBRES.  (Magnified  1000 
diameters. ) 

The  nerve  was  hardened  in  picric  acid 
and  stained  with  picro-carmine.  The 
radial  striation  of  the  medullary 
sheath  is  very  apparent.  In  one 
fibre  the  rays  are  broken  by  shrink- 
age of  the  axis-cylinder.  The  fibrils 
of  the  axis-cylinder  appear  tubular. 


FlG.  104. — A  SMALL  BUNDLE  OF 
NERVE-FIBRES  FROM  THE 
SYMPATHETIC  NERVE.  (Key 

and  Retzius.) 

The  bundle  is  composed  of  pale 
nerve-fibres,  with  the  exception 
of  the  fibre  m,  m,  which  is  in- 
closed here  and  there  by  a  thin 
medullary  sheath ;  n.  n,  nuclei 
of  pale  fibres. 


On  account  of  the  peculiar  refractive  power  of  the  medullary  sheath 
it  is  difficult  to  see  the  axis-cylinder  in  the  fresh  nerve  except  at  the 


1  According  to   Engelmaiin   the   axis-cylinder   is   not   structurally   continuous 
across  the  nodes  of  Ranvier. 


STRUCTURE  OF  NERVE-FIBRES. 


87 


nodes,  where  it  may  be  observed  stretching  across  the  interruption  in 
the  medullary  sheath,  and  it  may  also  sometimes  be  seen  projecting 
from  a  broken  end  of  a  nerve-fibre.  It  is  longitudinally  striated,  being 
really  made  up  of  exceedingly  fine  fibrils  (ultimate  fibrils,  fig.  102), 
which  are  darkly  stained  by  chloride  of  gold.  Staining  with  nitrate  of 
silver  produces  a  curious  transversely  striated  appearance  in  the  axis- 
cylinder,  but  it  is  not  known  if  this  indicates  a  pre-existent  structure. 
Kiihne  has  described  a  special  reticular  sheath  of  the  axis-cylinder 
lying  within  the  medullary  sheath,  and  composed  of  a  peculiar  chemical 
substance  termed  neurokeratin.  The  reticulum  is,  however,  produced 
within  the  substance  of  the  medullary  sheath,  probably  by  the  action 
of  reagents. 

Non-medullated  fibres. — Intermingled  with  the  medullated  fibres 
there  may  always,  even  in  the  cerebro-spinal  nerves,  be  found  a  certain 
number  of  pale  fibres  devoid  of  the  dark  double  contour  which  is 


FIG.  105.— SECTION  OF  A  PART  OF  THE  MEDIAN  NERVE  (HUMAN).      (DRAWN  AS  SEEN 
UNDER  A  LOW  MAGNIFYING  POWER.)     (From  Landois  after  Eichhorst.) 

ep,  epineurium,  or  general  sheath  of  the  nerve,  consisting  of  connective-tissue  bundles  of 
variable  size  separated  by  cleft-like  areolse,  with  here  and  there  blood-vessels  ;  pe,  lamel- 
lated  connective-tissue  sheaths  (perineurium)  of  the  funiculi ;  ed,  interior  of  funiculus, 
showing  the  cut  ends  of  the  medullated  nerve-fibres,  which  are  embedded  in  the  con- 
nective tissue  within  the  funiculus  (endoneurium). 

characteristic  of  the  presence  of  a  medullary  sheath.  There  are  the 
non-medullated  fibres,  also  called,  after  their  discoverer,  fibres  of  Remdk 
(fig.  104).  They  frequently  branch,  which  the  medullated  fibres 
never  do  except  near  their  termination,  and  they  are  beset  with 
numerous  nuclei  which  perhaps  belong  to  a  delicate  sheath.  The 


88 


THE  ESSENTIALS  OF  HISTOLOGY. 


sympathetic  nerves  are  largely  made  up  of  fibres  of  this  nature,  but, 
on  the  other  hand,  many  of  the  fibres  of  the  sympathetic  trunk  possess 
a  thin  medullary  sheath  (fig.  104). 

Structure  of  the  nerve-trunks. — In  their  course  through  the  body 
the   nerve-fibres  are  gathered   up   into   bundles  or  funiculi,  and   the 


FIG.  106.— PART  OF  A  SECTION  OF  ONE  OF  THE  FUNICULI  OF  THE  SCIATIC  NERVE  OF  MAN. 
(Key  and  Retzius. )      (Magnified. ) 

P,  perineurium  consisting  of  a  number  of  closely  arranged  lamella? ;  En,  processes  from  the 
perineurium,  passing  into  the  interior  of  the  funiculus,  and  becoming  continuous  with  the 
endoneurium,  or  delicate  connective  tissue  between  the  nerve-fibres.  The  connective- 
tissue  fibrils  of  the  endoneurium  are  seen  cut  across  as  tine  points,  often  appearing  to  en- 
sheath  the  nerve-fibres  with  a  circle  of  minute  dots  (fibril-sheath  of  Key  and  Retzius). 
Numerous  nuclei  of  connective-tissue  cells  are  embedded  in  the  endoneurium ;  v,  section 
of  a  blood-vessel. 

funiculi  may  again  be  united  together  to  form  the  nerves  which  we 
meet  with  in  dissection.  The  connective  tissue  which  unites  the 
funiculi  and  invests  the  whole  nerve,  connecting  it  to  neighbouring 


FIG.  107.  —  NERVE  -  FUNICULUS 
STAINED  WITH  NITRATE  OF  SIL- 
VER, SHOWING  THE  OUTLINES  OF 

EPITHELIOID-CELLS         OF         THE 

PERINEURIUM.     (Ranvier.) 

The  dark  crosses  on  the  nerve-fibres  at 
the  nodes  of  Ranvier  are  due  to  the 
staining  of  the  axis-cylinder  and  of 
a  band  of  intercellular  substance 
which  encircles  the  axis-cylinder  at 
the  node  (constricting  band  of  Ran- 
vier). 


parts  and  conveying  to  it  blood-vessels,  lymphatics,  and  even  nerve- 
fibres  destined  for  its  coats,  is  termed  the  epineurium  (fig.  105,  ep). 
That  which  ensheaths  the  funiculi  is  known  as  the  perineurium  (fig. 
105,  pe).  It  has  a  distinctly  lamellar  structure  (fig.  106,  p),  the  lamellae 


STRUCTURE  OF  NERVE- FIBEES.  89 

being  composed  of  connective  tissue  and  covered  on  both  surfaces  by 
flattened  epithelioid  cells  (fig.  107).  Between  the  lamellae  are  clefts  for 
the  conveyance  of  lymph  to  the  lymphatics  of  the  epineurium.  The 
delicate  connective  tissue  which  lies  between  the  nerve-fibres  of  the 
funiculus  is  the  endoneurium  (fig.  105,  ed;  fig.  106,  En).  It  assists  in 
supporting  the  longitudinally  arranged  meshwork  of  blood-capillaries, 
and  its  interstices  communicate  with  the  lymphatic  clefts  of  the 
perineurium. 

All  the  branches  of  a  nerve,  and  even  single  nerve-fibres  which  are 
passing  to  their  distribution,  are  invested  with  a  prolongation  of  the 
perineural  sheath,  which  is  there  known  as  the  sheath  of  Henle. 

The  nerve-trunks  themselves  receive  nerve-fibres  (nervi  nervomm) 
which  ramify  chiefly  in  the  epineurium  and  terminate  within  this  in 
end-bulbs  (Horsley). 


90  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSONS  XIX.  AND  XX. 

STRUCTURE  OF  GANGLIA;  STRUCTURE  OF  NERVE-CELLS 
OF  BRAIN  AND  SPINAL  CORD ;  NEUROGLIA  -  CELLS ; 
DEVELOPMENT  OF  NERVE  -  FIBRES ;  WALLER! AN  DE- 
GENERATION. 

1 .  PUT  a  small  piece  of  spinal  ganglion  into  1  per  cent,  osmic  acid  for  two  or 
three  hours.  Place  it  in  water  containing  a  fragment  of  thymol  for  two  days 
or  more.  Tease  it  in  dilute  glycerine.  Notice  the  spheroidal  ganglion-cells ; 
their  large  nuclei  and  distinct  nucleoli.  Many  of  the  cells  may  still  be  seen 
within  their  nucleated  membranous  sheath.  Look  for  cells  which  still  retain 
the  axis-cylinder  process  and  for  T-shaped  junctions  of  nerve-fibres  with  this. 

2.  Prepare  a  piece  of  sympathetic  ganglion  in  the  same  way.     Cells  may 
be  found  with  three  or  more  axis-cylinder  processes.    If  from  a  rabbit  observe 
that  many  of  the  cells  are  bi-nucleated. 

Measure  two  or  three  cells  in  each  of  the  above  preparations. 

3.  Mount  stained  sections  of  ganglia  in  Canada  balsam.     These  will  serve 
to  show  the  arrangement  of  the  cells  and  fibres  in  the  ganglion  and  the 
nucleated  sheaths  around  the  nerve-cells. 

4.  Tease  out  a  portion  of  the  grey  matter  from  a  piece  of  spinal  cord  that 
has  been  a  day  or  two  in  dilute  chromic  acid  (•£$  per  cent.),  or  in  30  per  cent, 
alcohol.     Or  a  little  of  the  grey  matter  may,  after  macerating  for  a  day  or 
two  in  either  of  the  above  fluids,  be  shaken  up  with  water  in  a  test  tube,  and 
after  standing  a  little  while  some  of  the  sediment  at  the  bottom  of  the  tube 
may  be  drawn  off  and  mounted.     Before  covering,  look  for  the  nerve-cells 
with  a  low  power,  and  if  possible  get  out  one  or  two  clear  of  the  surrounding 
substance.     Mount  in  water  with  a  thick  hair  under  the  cover-glass.    Notice 
the  large  branching  cells,  some  with  a  mass  of  pigment  near  the  nucleus. 
Observe   the   fibrillation   of   the   cell-processes.      Notice   also   the   reticular 
character   of   the   tissue   in   which   the   cells   are   embedded.      Many   axis- 
cylinders  will  be  seen  in  this  preparation  deprived  wholly  or  partially  of 
their  medullary  sheath,  and  their  fibrillar  structure  can  then  also  be  well 
seen.     Carefully  sketch  these  appearances.     To  keep  this  preparation  run 
solution  of  osmic  acid  under  the  cover-glass,  and  when  the  cells  are  stained 
allow  a  drop  of  glycerine  to  pass  in  by  diffusion.     Similar  preparations  are 
to  be  made  from  the  grey  matter  of  the  cerebral  cortex  and  cerebellar  cortex. 

5.  Examine  the  nerve-cells  and  neuroglia-cells  in  sections  from  the  spinal 
cord,  cerebrum,  and  cerebellum  of  a  small  animal,  e.g.  young  rat  or  kitten, 
prepared   by   Golgi's   method.1     The   sections   must   be   mounted   in  thick 

1  See  Appendix. 


STRUCTURE  OF  NERVE-CELLS.  91 

Canada  balsam  without  a  cover-glass,  and  the  balsam  dried  rapidly  on  a 
warm  plate. 

6.  Make  teased  preparations  from  a  nerve  which,  some  days  previously, 
has  been  cut  nearer  the  spinal  cord.  The  nerve  should  have  been  prepared 
with  osmic  acid,  as  in  Lesson  xviii.  sec.  3.  Notice  the  breaking  up  of  the 
my  el  in  of  the  medullary  sheath,  varying  in  degree  according  to  the  length  of 
time  the  section  has  been  made  previously.  In  preparations  from  the  central 
cut  end  of  the  nerve  new  fibres  may  be  seen  budding  from  near  the 
extremities  of  the  undegenerated  fibres  of  the  stump. 


Nerve-cells  only  occur  in  the  grey  matter  of  the  nerve-centres,  and 
in  little  groups  on  the  course  of  certain  of  the  peripheral  nerves,  these 
groups  often  causing  nodular  enlargements  of  the  nerves,  which  are 
known  as  ganglia.  The  most  important  ganglia  are  those  which  are 
found  upon  the  posterior  roots  of  the  spinal  nerves,  upon  the  roots  of 
some  of  the  cranial  nerves,  and  upon  the  trunk  and  principal  branches 
of  the  sympathetic  nerve.  Minute  ganglia  are  also  found  very  nume- 
rously in  connection  with  the  nerves  which  are  supplied  to  involuntary 
muscular  tissue,  as  in  the  heart,  alimentary  canal,  bladder,  uterus,  etc. 


FIG.  108A.— LONGITUDINAL  SECTION  THROUGH  THE  MIDDLE  OF  A  GANGLION  ON  THE 

POSTERIOE  ROOT  OF  ONE  OF  THE  SACRAL  NERVES  OF  THE  DOG,  AS  SEEN  UNDER  A 
LOW  MAGNIFYING  POWER. 

a,  nerve-root  entering  the  ganglion  ;  b,  fibres  leaving  the  ganglion  to  join  the  mixed  spinal 
nerve  ;  c,  connective-tissue  coat  of  the  ganglion  ;  d,  principal  group  of  nerve-cells,  with 
fibres  passing  down  from  amongst  the  cells,  probably  to  unite  with  the  longitudinally 
coursing  nerve-fibres  by  "T-shaped  junctions. 

Nerve-cells  vary  much  in  size  and  shape ;  many  are  large,  some  being 
amongst  the  largest  cells  met  with  in  the  body,  but  others  are  quite 
small.  The  nucleus  is  generally  large,  clear,  and  spherical,  with  a 
single  large  and  distinct  nucleolus ;  there  is  also  a  network  of  chromo- 
plasm.  The  shape  depends  a  good  deal  on  the  number  of  processes, 
and  the  manner  in  which  they  come  off  from  the  cell.  If  there  is  but 
one  process  the  cell  is  generally  nearly  spherical.  This  is  the  case  with 


92  THE  ESSENTIALS  OF  HISTOLOGY. 

the  cells  of  the  spinal  ganglia  (fig.  108);  in  these  the  single  process, 
after  a  short  course,  joins  one  of  the  nerve-fibres  which  is  traversing 


FIG.  lOSu. — CELL  FROM  A  SPINAL  GANGLION.     (Retziua.) 

xh,  nucleated  sheath  of  the  cell ;  n,  n',  the  nerve-fibre  which  the  single  process  of  the  cell, 
after  a  number  of  coils,  joins. 

the  ganglion.     When  there  are  two  processes,  they  often  go  off  in 
opposite  directions  from  the  cell,  which  is  thus  rendered  somewhat 


FIG.  109A.  -SYMPATHETIC  GANGLION- 
CELL  OF  A  FROG,  HIGHLY  MAGNI- 
FIED. (Beale.) 

a,  a,  straight  fibre  ;  b,  b,  coiled  fibre, 
dividing  as  it  passes  to  the  cell. 


FIG.      109B.  —  A      GANGLION-CELL      WITHIN      ITS 
SHEATH  ;     FROM     THE     HUMAN      SYMPATHETIC. 

(Key  and  Retzius.)     (Highly  magnified.) 


spindle-shaped,  but  occasionally  they  emerge  at  the  same  part.     In 
some  cases  where  there  appear  to  be  two  fibres  connected  with  a  cell, 


STRUCTUEE  OF  NERVE-CELLS. 


93 


one  of  them  is  really  derived  from  another  nerve-cell  elsewhere,  and  is 
passing  to  end  in  a  ramification  which  envelops  the  ganglion-cell ;  it 
may  be  coiled  spirally  around  the  issuing  nerve-process  as  in  fig.  109A. 
When  there  are  three  or  more  processes,  the  cell  becomes  irregularly 
angular  or  stellate.  Sometimes,  as  in  the  sympathetic  ganglia  (fig. 
109B),  all  the  processes  appear  to  become  nerve-fibres,  but  in  other 
instances,  as  in  the  large  cells  of  the  grey  matter  of  the  spinal  cord  and 
of  the  brain,  only  one  process  becomes  the  axis-cylinder  of  a  nerve-fibre 
(process  of  Deiters),  the  others  dividing  and  subdividing  in  a  ramified 
manner  (dendrifes),  until  they  end  in  an  arboresence  of  fine  twigs. 


FIG.  110.— NERVE-CELL  FROM  SPINAL  CORD  OF  ox,  ISOLATED  AFTER  MACERATION 
IN  VERY  DILUTE  CHROMIC  ACID.      (Magnified  175  diameters.) 

The  cell  has  a  well-defined,  clear,  round  nucleus,  and  a  large  nucleolus.  The  cell-processes 
are  seen  to  be  finely  fibrillated,  the  fibrils  passing  from  one  process  into  another  through 
the  body  of  the  cell.  «,  axis-cylinder  process  broken  a  short  distance  from  the  cell. 

According  to  the  number  of  their  processes,  nerve-cells  are  termed 
uni-,  bi-,  or  multi-polar. 

In  the  ganglia  the  nerve-cells  have  a  nucleated  sheath  (figs.  108B, 
109)  which  is  continuous  with  the  sheath  of  the  nerve-fibres  with 
which  they  are  connected.  In  the  spinal  ganglia,  and  in  many  of 
the  ganglia  at  the  roots  of  the  cranial  nerves,  the  cells  are  unipolar,  and 
the  cell -process  joins  a  traversing  nerve-fibre  by  a  T-shaped  junction 
(fig.  10 SB).  In  the  sympathetic  ganglia  they  are  usually  multipolar 
(fig.  109B).  The  cells  are  disposed  in  aggregations  of  different  size 


94 


THE  ESSENTIALS  OF  HISTOLOGY. 


separated  by  the  bundles  of  nerve-fibres  which  are  traversing  the 
ganglion  (fig.  108A).  The  ganglion  if  large  is  inclosed  by  an  investing 
capsule  of  connective  tissue  which  is  continuous  with  the  epi-  and  peri- 
neurium  of  the  entering  and  issuing  nerve-trunks. 

Many  nerve-cells,  and  notably  those  of  the  spinal  cord,  have  a  finely 
fibrillar  structure.  The  fibrils  can  be  traced  into  the  branches  of  the 
cells  and  into  the  axis-cylinders  of  nerve-fibres  which  are  connected 

with  the  cells  (fig.  110).  Other- 
wise the  cells  have  a  finely 
granular  appearance ;  often  with 
a  clump  of  black,  brown,  or 
yellow  pigment-granules  placed 
at  one  side  of  the  nucleus. 

In  preparations  made  by 
Golgi's  nitrate  of  silver  method 
the  nerve-cells  and  their  pro- 
cesses are  coloured  black  by  a 
deposit  of  reduced  silver,  so  that 
the  processes  can  be  traced  for 
a  considerable  distance  from  the 
body  of  the  cell,  in  fact  in  some 
instances  as  far  as  their  remotest 
ramifications  (fig.  112).  It  is 
found  by  the  employment  of 
this  method  that  the  axis- 
cylinder  process  is  not  always 
an  unbranched  process,  as  was 
formerly  supposed,  but  that  it 
usually,  if  not  invariably,  gives 
off  fine  lateral  branches  (col- 
laterals), which  themselves  tend 
to  ramify  in  the  adjacent  nerve- 
substance.  And,  although  the 
main  part  of  the  axis-cylinder 

FlG.  111. —MULTIPOLAR  NERVE-CELL  FROM  AN-    -.-ntH***     nanalKr     nnc  f\n     anrl 

TERIOR   HORN   OF   SPINAL    CORD,   HUMAN.   P™cess  usually  passes   on  and 
(Gerlach.)  becomes  part  of  a  long  medul- 

«,  Axis-cylinder  or  nerve-fibre  process;  6,  pigment.     ^^    nerye.fibre    (firgt    type    of 

Grolgi),  this  is  not  always  the  case,  for  in  another  type  of  nerve-cell 
within  the  nerve-centres  (second  type  of  Grolgi),  the  axis-cylinder 
process  breaks  up  after  a  short  course  into  a  terminal  arboresence, 
which  usually  envelops  other  nerve-cells. 

Moreover,  even  the  long  process  of  type  1  (which  becomes  the  axis- 


STRUCTURE  OF  NERVE-CELLS. 


95 


cylinder  of  a  long  nerve-fibre)  ultimately  ends  in  a  similar  manner, 
that  is  to  say,  in  a  terminal  ramification  or  arborescence,  as  will  be  seen 


FIG.  112.— FROM  A  SECTION  OF  CEREBRAL  CORTEX  OF  A  YOUNG  RABBIT,  PREPARED  BY 

GOLGl's  METHOD.      (G.  Retzius.) 
g,  nerve-cells  ;  /i,  neuroglia-cells ;  a,  axis-cylinder  processes  of  nerve-cells. 


96  THE  ESSENTIALS  OF  HISTOLOGY. 

in  studying  the  endings  of  nerve-fibres,  and  the  structure  of  the  central 
nervous  system. 

It  is  further  shown  by  this  method  that  each  nerve-cell  is  an  ana- 
tomically  independent   element,    consisting   of  the   cell-body  with   its 


—p 

-my 

—vty 
-ff 


FIG.  113. — DEGENERATION  AND  REGENERATION  OF  NERVE-FIBRES  IN  THE  RABBIT. 

(Ranvier. ) 

A,  part  of  a  nerve-fibre  in  which  degeneration  has  commenced  in  consequence  of  the  section, 
fifty  hours  previously,  of  the  trunk  of  the  nerve  higher  up  ;  my,  medullary  sheath  be- 
coming broken  up  into  drops  of  myelin  ;  p,  granular  protoplasmic  substance  which  is 
replacing  the  myelin  ;  n,  nucleus  ;  g,  primitive  sheath.  B,  another  fibre  in  which 
degeneration  is  proceeding,  the  nerve  having  been  cut  four  days  previously ;  p,  as 
before  ;  cy,  axis-cylinder  partly  broken  up,  and  the  pieces  inclosed  in  portions  of  myelin. 
C,  more  advanced  stage  of  degeneration,  the  medullary  sheath  having  almost  disappeared, 
and  being  replaced  by  protoplasm  in  which,  besides  drops  of  myelin,  are  numerous 
nuclei  which  have  resulted  from  the  division  of  the  single  nucleus  of  the  internode.  D, 
commencing  regeneration  of  a  nerve-fibre.  Several  small  fibres,  t't",  have  sprouted  from 
the  somewhat  bulbous  cut  end,  6,  of  the  original  fibre,  t  ;  a,  an  axis-cylinder  which  h.is 
not  yet  acquired  its  medullary  sheath  ;  s,  «',  primitive  sheath  of  the  original  fibre.  A,  C, 
and  D  are  from  osmic  preparations  ;  B  from  an  alcohol  and  carmine  preparation. 

nucleus,  the  ramified  "protoplasmic"  processes  or  dendrites,  and  the 
•tierve-process  which  becomes  the  axis-cylinder  of  a  nerve-fibre.  It  will 
therefore  be  easily  understood  that  when  a  nerve  is  cut,  part  of  the 
axis-cylinder  will  be  cut  off  from  the  cell  to  which  it  belongs,  and  from 


STRUCTURE  OF  NEUROGLIA.  97 

which  it  has  grown.  This  separated  part  of  the  axis-cylinder  dies,  and 
its  medullary  sheath  undergoes  a  gradual  process  of  disintegration  into 
droplets  of  myelin,  which  is  known  as  the  Wallerian  degeneration  (fig. 
113,  A  to  C),  and  which  in  man  and  mammals  begin  about  two  or 
three  days  after  section  of  the  nerve.  Therefore  when  a  peripheral 
nerve  is  cut,  all  the  nerve-fibres  distal  to  the  point  of  section  must 
degenerate,  because  all  have  grown  from  and  are  connected  with  nerve- 
cells  in  or  near  the  nerve  centre — the  afferent  fibres  with  the  cells  of 
the  ganglion  on  the  posterior  root,  the  efferent  fibres  with  the  cells  of 
the  anterior  horde  of  the  spinal  cord. 

If  regeneration  takes  place  in  the  cut  nerve,  it  is  effected  not  by  a 
re-establishment  of  connection  between  the  degenerated  fibres  and  those 
of  the  central  stump  (which  are  not  degenerated),  but  by  an  outgrowth 
of  new  fibres  from  the  stump  (fig.  113,  D) ;  these  may  find  their  way 
to  the  periphery  along  the  course  of  the  degenerated  fibres.  If  they 
succeed  in  doing  so,  the  continuity  and  conducting  power  of  the  nerve 
becomes  restored. 

In  the  brain  and  spinal  cord  the  nerve-cells  and  nerve-fibres  are 
supported  by  a  peculiar  tissue  which  has  been  termed  the  neuroglia. 
It  is  composed  of  cells  and  fibres,  the  latter  being  prolonged  from  the 
cells.  Of  the  fibres  some  are  radially  disposed.  They  start  from  the 
fixed  ends  of  the  ciliated  epithelium-cells  which  line  the  central  canal  of 
the  spinal  cord  and  the  ventricles  of  the  brain,  and  pass  in  a  radial 
direction,  slighting  diverging  as  they  proceed,  and  constantly  branching 
towards  the  surface  of  the  organ,  where  they  end  in  slight  enlargements 
attached  to  the  pia  mater.  The  other  fibres  of  the  tissue  are  cell-pro- 
cesses of  the  neuroglia-  or  glia-cells  proper  (spider-cells).  These  cells 
are  stellate  in  shape  (fig.  Ill,  n],  and  their  fine  and  frequently  ramifying 
processes  pass  as  neuroglia-fibres  between  the  nerve-cells  and  nerve- 
fibres  which  they  aid  in  supporting. 


98  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  XXI. 

MODES  OF  TERMINATION  OF  NERVE-FIBRES. 

1.  SHELL  out  a  Pacinian  corpuscle  from  a  piece  of  cat's  mesentery  which  has 
been  kept  for  two  or  three  days  in  ^  per  cent,  chromic  acid  or  30  per  cent, 
alcohol,  and  clear  it  as  much  as  possible  of  adhering  fat,  but  be  careful  not  to 
prick  or  otherwise  injure  the  corpuscle  itself.  Mount  in  water  with  a 
thick  hair  to  prevent  crushing  with  the  cover-glass.  Sketch  the  corpuscle 
under  a  low  power,  and  afterwards  draw  under  a  high  power  the  part  of  the 
core  where  the  nerve  enters  and  the  part  where  it  terminates.  Notice  the 
fibrous  structure  of  the  lamellar  tunics  of  the  corpuscle  and  the  oval  nuclei 
belonging  to  flattened  endothelial-cells  which  cover  the  tunics.  The  distinct 
lines  which  when  seen  in  the  fresh  corpuscle  are  generally  taken  for  the 
tunics,  are  really  the  optical  sections  of  these  flattened  cells. 

2.  Mount  in  dilute  .glycerine  one  or  more  sections  of  a  rabbit's  cornea 
which  has  been  stained  with  chloride  of  gold.     Notice  the  arrangement  in 
plexuses  of  the  darkly-stained  nerve-fibres  and  fibrils,  (1)  in  the  connective- 
tissue  substance,  (2)  under  the  epithelium,  and  (3)  between  the  epithelial- 
cells.     Make  one  or  two  sketches  showing  the  arrangement  of  the  fibrils. 

3.  Spread  out  a  small  piece  of  muscle  which  has  been  stained  with  chloride 
of  gold  by  Lowit's  method,  and  examine  it  with  a  low  power  to  find  the 
nerve-fibres  crossing  the  muscular  fibres  and  distributed  to  them. 

Try  and  separate  those  parts  of  the  muscular  fibres  to  which  nerves 
appear  to  go,  and  mount  them  in  glycerine.  The  pieces  of  muscle  may 
advantageously  be  thinned  out  for  observation  by  pressure  upon  the  cover- 
glass.  Search  thoroughly  for  the  close  terminal  ramifications  (end-plates) 
of  the  axis-cylinders  immediately  within  the  sarcolemma. 

It  is  rather  difficult  to  dissociate  the  fibres,  and  much  patience  is  some- 
times required  in  searching  for  the  nerve-terminations,  but  when  they  are 
found  the  trouble  is  amply  repaid.1 


Modes  of  ending  of  sensory  nerve-fibres. — Nerve-fibres  which  are 
distributed  to  sensory  parts  end  either  in  special  organs  or  in  free 
terminal  ramifications.  Within  the  special  organs  the  ending  is  also 
usually  ramified.  There  are  three  chief  kinds  of  special  organs,  termed 
respectively  Pacinian  corpuscles,  tactile  corpuscle*,  and  emi-bulbs.  In  the 
tactile  corpuscles  and  end-bulbs  the  connective-tissue  sheath  of  a 
medullated  fibre  expands  to  form  a  solid  bulbous  enlargement,  which  is 
cylindrical  or  spheroidal  in  the  end-bulbs  and  ellipsoidal  in  the  tactile 
corpuscles.  In  both  kinds  of  end-organ  there  is  a  capsule  of  connective- 

1  For  methods  of  staining  with  chloride  of  gold  see  Appendix.  The  methyl-blue  method 
of  Ehrlich,  which  is  often  employed  to  study  these  and  other  modes  of  nerve-termina- 
tion, will  also  be  found  in  the  Appendix. 


MODES  OF  TERMINATION  OF  NERVE-FIBRES.  99 

tissue  within  which  is  generally  a  sort  of  core  containing  numerous 


FIG.  114.  -SECTION  OF  SKIN  SHOWING  TWO  PAPILLA  AND  DEEPER  LAYERS  OF 
EPIDERMIS.     (Biesiadecki. ) 

vascular  papilla  with  capillary  loop  passing  from  subjacent  vessel,  c ;  b,  nerve-papilla  with 
tactile  corpuscle,  t.  The  latter  exhibits  transverse  fibrous  markings  ;  d,  nerve  passing  up 
to  it ;  /,  /,  sections  of  spirally  winding  nerve-fibres. 


FIG.  115. — TACTILE  CORPUSCLE  WITHIN 

A    PAPILLA    OF    THE     SKIN    OF    THE 
HAND,  STAINED  WITH  CHLORIDE  OF 

GOLD.     (Ranvier. ) 

n,  two  nerve-fibres  passing  to  the  cor- 
puscle ;  a,  a,  varicose  ramifications  of 
theaxis-cylinders  within  the  corpuscle. 


FIG.  116.— SIMPLE  TACTILE 
END-ORGANS  FROM  THE 
CLITORIS  OF  THE  RABBIT. 
(Izquierdo. ) 


100 


THE  ESSENTIALS  OF  HISTOLOGY. 


nucleated  cells.     As  the  nerve-fibre  enters  the  corpuscle  (which  in  the 
tactile  corpuscle  only  happens  after  it  has  reached  the  distal  part  of  the 


FIG.  117. — CYLINDRICAL 

END-BULB     FROM     THE 
CONJUNCTIVA    OP    THE 

CALF.     (Merkel. ) 


FIG.  118. — END-BULB  FROM  THE  HUMAN 
CONJUNCTIVA.  (Longworth.) 

a,  nucleated  capsule  ;  b,  core,  the  outlines  of 
its  cells  are  not  seen ;  c,  entering  fibre- 
branching.  and  its  two  divisions  passing  to 
terminate  in  the  core  at  d. 


corpuscle,  having  wound  spirally  once  or  twice  round  it)  it  loses  its 
sheaths  and  is  prolonged  as  an  axis-cylinder  only,  which  terminates 


FIG.  119.— END- 
BULB  FROM  THE 
HUMAN  CONJUNC- 
TIVA, TREATED 
WITH  ACETIC  ACID 
AND  OSMIC  ACID. 

A£o.  (W.  Krause) 


FIG.    121. — COMPOUND 

END-BULB  FROM  THE 
CLITORIS,          HUMAN. 

(W.  Krause.) 


FIG.  120. — ARTICULAR  CORPUSCLE, 
HUMAN.    £££.     (W.  Krause.) 


after  either  a  straight  or  a  convoluted  course  within  the  organ  (see 
figs.  115  to  118).  Tactile  corpuscles  occur  in  some  of  the  papillae  of 
the  skin  of  the  hand  and  foot,  in  sections  of  which  they  will  be 


MODES  OF  TERMINATION  OF  NERVE-FIBRES.  101 

afterwards    studied.       End-bulbs    are    found    in    the    conjunctiva    of 
the   eye,    where  in  most  animals  they  have  a  cylindrical  or  oblong 
shape   (fig.    117),   but  in  man  are  spheroidal  (fig.   118).     They  have 
also    been    found    in    papillae    of    the    lips    and   tongue,   and    in    the 
epineurium  of  the  nerve-trunks,   and  somewhat  similar  sensory  end-_ 
organs  also  occur  in  the  integument  of  the  external  genital  organs  of 
both  sexes  (figs.  116,  121).     Similar 
bodies  of  larger  size  are  also  met 
with  in  the    neighbourhood  of  the 
joints    (fig.     120).       In    the     skin 
covering  the  bills  of  certain  birds 
{e.g.   duck),   a  simple  form  of  end- 
organ  occurs,  consisting  of  two  or 
more  cells  arranged  in  rows  within  a    FIG.  122.— TACTILE  CORPUSCLES  FROM  THE 
capsule,  with  the  axis-cylinder  ter-  DUCK'S  TONGUE.    (Izquierdo.) 

f,                                       .  A,  composed  of  three  cells,  with  two  inter- 

minatmg     in      flattened     expansions  posed  disks,  into  which  the  axis-cylinder  of 

i      .                    ,i_              IT        /                7             x  the  nerve,  w,  is  observed  to  pass  ;  in  B  there 

between      the       Cells      (COrpUSCleS      OJ  is  but  one  tactile  disk  inclosed  between  two 

Grandry,  fig.  122). 

The  Pacinian  corpuscles  are  larger,  and  have  a  more  complex 
structure,  than  the  tactile  corpuscles  and  end-bulbs  (fig.  123).  They 
.are  composed  of  a  number  of  concentric  coats  arranged  like  the  layers 
of  an  onion,  and  inclosing  the  prolonged  end  of  a.  nerve-fibre.  A  single 
medullated  nerve-fibre  goes  to  each  Pacinian  corpuscle  encircled  by 
-a  prolongation  of  perineurium,  and  within  this  by  endoneurium ;  when 
it  reaches  the  corpuscle,  of  which  it  appears  to  form  the  stalk,  the 
lamellae  of  the  perineurium  expand  to  form  some  of  the  tunics  of  the 
corpuscle.  The  nerve  passes  on,  piercing  the  other  tunics,  and  still 
provided  with  medullary  sheath,  and  surrounded  by  endoneurium,  to 
reach  the  centre  of  the  corpuscle.  Here  the  endoneurium  is  prolonged 
to  form  a  sort  of  core  of  cylindrical  shape,  along  the  middle  of  which 
the  nerve-fibre,  now  deprived  of  its  medullary  and  primitive  sheaths, 
passes  in  a  straight  course  as  a  simple  axis-cylinder  (figs.  123,  ri ;  124, 
'•./. )  to  terminate  at  the  farther  end  of  the  core,  either  in  an  arborisation 
or  in  a  bulbous  enlargement. 

The  tunics  of  the  corpuscle  are  composed  of  connective  tissue,  the 
fibres  of  which  for  the  most  part  run  circularly.  They  are  covered  on 
both  surfaces  with  a  layer  of  flattened  endothelial-cells,  and  here  and 
there  cleft-like  lymph-spaces  can  be  seen  between  them  like  those 
between  the  layers  of  the  perineurium  (see  p.  88). 

When  sensory  nerve-fibres  terminate  in  plexuses,  they  generally 
branch  once  or  twice  on  nearing  their  termination.  ,  The  sheaths  of  the 
fibres  then  successively  become  lost,  first  the  connective  tissue  or  peri- 


102 


THE  ESSENTIALS  OF  HISTOLOGY. 


neural  sheath,   then  the  medullary  sheath,   and  lastly  the   primitive 
sheath,  the  axis-cylinder  being  alone  continued  as  a  bundle  of  primitive 


FIG.  123. — MAGNIFIED  VIEW  OF  A  PACINIAN  BODY  FROM  THE  CAT'S  MESENTERY. 

(Ranvier.) 

n,  stalk  of  corpuscle  with  nerve-fibre  inclosed  in  sheath  of  Henle  passing  to  the  corpuscle ; 
n',  its  continuation  through  the  core,  m,  as  axis-cylinder  only ;  a,  its  terminal  arborisa- 
tion ;  c,  d,  sections  of  endothelial-cells  of  tunics,  often  mistaken  for  the  tunics  themselves ; 
/,  channel  through  the  tunics  which  expands  into  the  core  of  the  corpuscle. 

fibrils  (fig.   125,  n).     This  branches  and  joins  with  the  ramifications, 
of  the  axis-cylinders  of  neighbouring  nerve-fibres  to  form  a  primary 


MODES  OF  TERMINATION  OF  NERVE-FIBRES. 


103 


plexus.  From  the  primary  plexus  smaller  branches  (a)  come  off,  and 
these  form  a  secondary  plexus  (e)  nearer  the  surface,  generally  imme- 
diately under  the  epithelium  if  the  ending  is  in  a  membrane  covered  by 
that  tissue.  Finally,  from  the  secondary  plexus  nerve-fibrils  proceed 
and  form  a  terminal  plexus 
or  ramification  amongst  the 
epithelium-cells  (fig.  126,  p), 
the  actual  ending  being  gene- 
rally in  free  varicose  fibrils  (I). 
Such  a  mode  of  ending  in  ter- 
minal plexuses  is  most  char- 
acteristically seen  in  the  cornea 
of  the  eye.  The  nerve-fibrils  p&. 
may  be  brought  distinctly 
into  view  by  staining  with 
chloride  of  gold,  and  then  the 
fibrillar  structure  of  the  rami- 
fications of  the  axis-cylinders 
also  becomes  very  apparent. 

Nerve-endings  in  tendons.— 
A  special  modification  of  the 
terminal  plexus  is  met  with 
in  many  of  the  tendons,  near 
the  points  of  attachment  of 
the  muscular  fibres.  The 


Ttt.S 


FIG.   124.— PART  OF  PACINIAN  BODY,    SHOWING 

THE    NERVE-FIBEE    ENTERING   THE    CORE.      FROM 

tendon-bundles  are  somewhat      AN  OSMIC  ACID  PREPARATION. 

ms,  entering  nerve-fibre,  the  medullary  sheath  of  which 
is  stained  darkly,  and  ends  abruptly  at  the  core ; 
ps,  prolongation  of  primitive  sheath,  passing  towards 
the  outer  part  of  the  core  ;  c.f,  axis-cylinder  passing 
through  the  core  of  the  central  fibre  ;  e,  some  of  the 
inner  tunics  of  the  corpuscle,  enlarged  where  they 
abut  against  the  canal  through  which  the  nerve-fibre 
passes— the  dots  within  them  are  sections  of  the 
fibres  of  which  they  are  composed  ;  n,  nuclei  of  the 
tunics  ;  n',  nuclei  of  the  endoneurium,  continued  by 
others  in  the  outer  part  of  the  core. 


enlarged,  and  the  nerve-fibres 

— one,  two,  or  even  more  in 

number — pass  to  the  enlarged 

part,  and  penetrating  between 

the    fasciculi    of    the   tendon 

end  in  a  terminal  arborisation, 

beset  with  irregular  varicosities.     The  whole  structure,  including  the 

enlargement  of  the  tendon-bundle  in  which  the  aborisation  occurs,  is 

known  as  the  organ  of  Golgi  (fig.  127). 

Ending  of  motor  nerves. — Lastly  the  nerves  to  muscles  also  ter- 
minate in  plexuses,  which  in  striated  (voluntary)  muscles  are  collected 
into  special  organs  termed  motor  end-organs,  or,  incorrectly,  end-plates. 

In  involuntary  muscle,  the  nerve-fibres,  which  near  their  termination 
are  entirely  non-medullated,  end  in  plexuses.  The  primary  plexuses 
are  generally  furnished  with  ganglion-cells  in  abundance.  From  these 
other  nerve-fibres  pass  which  form  secondary  plexuses  and  terminal 


104 


THE  ESSENTIALS  OF  HISTOLOGY. 


ramifications  amongst  the  contractile   fibre-cells.      These  nerves  will 
be  more  fully  studied  in  connection  with  the  intestine. 


FIG.  125. — SUB-EPITHELIAL  PLEXUS  OF  THE  CORNEA  TREATED  WITH  CHLORIDE  OF 
GOLD.     (Ranvier.) 

n,  branch  of  primary  plexus  ;  a,  small  branch  passing  to  join  the  sub-epithelial  plexus,  e. 

Jl  b 


FIG.  126. — VERTICAL  SECTION  OF  CORNEA  STAINED  WITH  CHLORIDE  OF  GOLD. 

(Ranvier.) 

/',  /•,  primary  plexus  in  connective  tissue  of  cornea  ;  a,  branch  passing  to  sub-epithelial  plexus,  ,<t ; 
p,  intra-epithelial  plexus  ;  6,  terminations  of  fibrils. 

In  voluntary  muscle  the  nerves,  which  are  always  medullated,  ter- 
minate in  special  motor  end-organs.     A  medullated  fibre  will  branch 


MODES  OF  TERMINATION  OF  NEEVE-FIBRES. 


105 


two  or  three  times  before  ending,  and  then  each  branch  passes  straight 
to  a  muscular  fibre.  Having  reached  this,  the  neurolemma  of  the 
nerve-fibre  is  continued  into  the  sarcolemma  of  the  muscle,  the  medul- 
lary sheath  stops  short,  and  the  axis-cylinder  ends  in  a  close  terminal 
ramification  with  varicosities  upon  its  branches  (figs.  128,  129).  This 
rj unification  is  embedded  in  a  layer  of  granular  nucleated  protoplasm. 
In  some  cases  the  ramification  is  restricted  to  a  small  portion  of  the 


FIG.  127. — OKGAN  OF  GOLGI  FROM  THE  HUMAN  TENDON  ACHILLES.    CHLORIDE  OF  GOLD 

PREPARATION.      (Ciaccio.) 
HI,  muscular  fibres  ;  t,  tendon-bundles  ;  G,  Golgi's  organ ;  n,  two  nerve-fibres  passing  to  it. 


FIG.  128.— NERVE-ENDING  IN  MUSCULAR  FIBRE  OF  A  LIZARD  (Lacerta  viridis). 

(Kiihne.) 

«,  end-plate  seen  edgeways  ;  6,  from  the  surface;  s,  s,  sarcolemma;  p,  p,  expansion  of  axis- 
cylinder.  In  6  the  expansion  of  the  axis-cylinder  appears  as  a  clear  network  branching 
from  the  divisions  of  the  medullated  fibres. 

muscular  fibre,  and  forms  with  the  granular  bed  a  slight  prominence 
(eminence  of  Doyere).  This  is  the  case  in  insects  and  mammals.  In  the 
lizard  the  ramification  is  rather  more  extended  than  in  mammals,  whilst 
in  the  frog  it  is  spread  over  a  considerable  length  of  the  fibre.  In 


106 


THE  ESSENTIALS  OF  HISTOLOGY. 


mammals  there  appears  to  be  only  one  end-plate  to  each  fibre,  while  in 
reptiles  there  may  be  several.  The  end-plate  is  covered,  external  to 
the  sarcolemma,  by  an  expansion  of  the  sheath  of  Henle  of  the  nerve- 
fibre. 


FIG.  129.— TERMINAL  RAMIFICATIONS  OF  THE  AXIS-CYLINDER  IN  END-ORGANS  OK 
MUSCLE,  STAINED  WITH  CHLORIDE  OF  GOLD.  (Ranvier.)  The  varicosities  here 
seen  are  probably  produced  by  the  reagent. 


STRUCTURE  OF  THE  LARGER  BLOOD-VESSELS.  101; 


LESSON  XXII. 


STRUCTURE  OF  THE  LARGER  BLOOD-VESSELS. 

1.  SECTIONS  of  a  medium-sized  peripheral  artery  and  vein,  e.g.  popliteal  or 
radial.  In  this  preparation  the  limits  of  the  vascular  coats  can  be  well  seen 
and  also  the  differences  which  they  present  in  the  arteries  and  veins  respec- 
tively. The  sections  may  be  stained  with  hsematoxylin  and  mounted  in 
Canada  balsam. 

2.  Mount  in  Canada  balsam  a  thin  slice  cut  from  the  inner  surface  of  an 
artery  which,  after  having  been  cut  open  longitudinally  and  washed  with 
distilled  water,  has  been  rinsed  with  nitrate  of  silver  solution  and  exposed  to 
the  light  in  spirit.     This  preparation  will  show  the  outlines  of  the  eiido- 
thelium-cells  which  line  the  vessel. 

3.  A  piece  of  an  artery  which  has  been  macerated  for  some  days  in  30  per 
cent,  alcohol  (1  part  rectified  spirit  to  two  parts  water)  is  to  be  teased  so  as 
to  isolate  some  of  the  muscular  cells  of  the  middle  coat  and  portions  of  the 
elastic  layers  (networks  and  fenestrated  membranes)  of  the  inner  and  middle 
coats.     The  tissue  may  be  stained  cautiously  with  diluted  haematoxylin,  and 
glycerine  afterwards  added.     The  muscular  cells  are  recognisable  by  their 
irregular  outline  and  long  rod-shaped  nucleus.     Sketch  one  or  two  and  also  a 
piece  of  fenestrated  membrane. 

4.  Transverse  sections  of  aorta  and  carotid.  Notice  the  differences  in  struc- 
ture between  these  and  the  section  of  the  smaller  artery. 

5.  Transverse  section  of  vena  cava  inferior.     Notice  the  comparatively 
thin  layer  of  circular  muscle,  and  outside  this  the  thick  layer  of  longitudinal 
muscular  bundles. 

Make  sketches  from  1,  4,  and  5  under  a  low  power,  from  2  and  3  under 
a  high  power. 


An  artery  is  usually  described  as  being  composed  of  three  coats, 
an  inner  or  elastic,  a  middle  or  muscular,  and  an  external  or  areolar 
(fig.  130,  b,  c,  d).  It  would,  however,  be  more  correct  to  describe  the 
wall  of  an  artery  as  being  composed  of  muscular  and  elastic  tissue 
lined  internally  by  a  pavement-epithelium  (endothelium)  and  strength- 
ened externally  by  a  layer  of  connective  tissue.  For  the  present,  how- 
ever, we  may  adhere  to  the  generally  received  mode  of  description. 
The  inner  coat  of  an  artery  is  composed  of  two  principal  layers.  The 
inner  one  is  a  thin  layer  of  pavement-epithelium  or  endothelium,  the  cells 
of  which  are  somewhat  elongated  in  the  direction  of  the  axis  of  the 
vessel  (fig.  131),  and  form  a  smooth  lining  to  the  tube.  After  death 


108 


THE  ESSENTIALS  OF  HISTOLOGY. 


they  become  easily  detached.  Next  to  this  comes  an  elastic  layer  in 
the  form  either  of  elastic  networks  (fig.  133)  or  of  a  fenestrated  membrane 
(fig.  132).  In  some  arteries  there  is  a  layer  of  fine  connective  tissue 
intervening  between  the  epithelium  and  the  fenestrated  membrane  (sub- 
epithelial  layer). 


FIG.  130.— TRANSVERSE  SECTION  OF  PART  OF  THE  WALL  OF  THE  POSTERIOR  TIBIAL 
ARTERY.     (75  diameters.) 

a,  epithelial  and  sub-epithelial  layers  of  inner  coat ;  b,  elastic  layer  (fenestrated  membrane) 
of  inner  coat,  appearing  as  a  bright  line  in  section  ;  c,  muscular  layer  (middle  coat) ;  d, 
outer  coat,  consisting  of  connective-tissue  bundles.  In  the  interstices  of  the  bundles 
are  some  connective  tissue  nuclei,  and,  especially  near  the  muscular  coat,  a  number  of 
elastic  fibres  cut  across. 


FIG.  131.— EPITHELIAL  LAYER  LINING 
THE  POSTERIOR  TIBIAL  ARTERY. 
(250  diameters.) 


Fig.  132.— PORTION  OF  FENESTRA- 

TEU  MEMBRANE  OF    HENLE   FROM 
AN    4RTERY.      (Toldt.) 


The  middle  coat  consists  mainly  of  circularly  disposed  plain  muscular 
fibres,  but  it  is  also  pervaded  in  most  arteries  by  a  network  of  elastic 
fibres  which  are  connected  with  the  fenestrated  membrane  of  the  inner 
coat  and  are  sometimes  almost  as  much  developed  as  the  muscular 
tissue  itself.  This  is  especially  the  case  with  the  larger  arteries  such 


STRUCTURE  OF  THE  LARGER  BLOOD-VESSELS.  10£ 

as  the  carotid  and  its  immediate  branches,  but  in  the  smaller  arteries  of 
the  limbs  the  middle  coat  is  almost  purely  composed  of  muscular  tissue. 
The  muscular  fibres  are  comparatively  short,  with  long  rod-shaped 
nuclei,  and  are  often  irregular  in  shape  (as  in  fig.  134). 


FIG.  133.— ELASTIC  NET- 
WORK OF  ARTERY. 
(Toldt.) 


FIG.  134. — MUSCULAR  FIBRE-CELLS  FROM 

SUPERIOR    THYROID   ARTERY.      (340  dia 

meters. ) 


FIG.  135.— SECTION  OF  THORACIC  AORTA  AS  SEEN  UNDER  A  LOW  POWER.    (Toldt.) 

a.  the  inner  coat  consisting  of  three  layers,  viz. :  1.  Epithelium  seen  as  a  fine  line.     2.  Sub- 
'    epithelial.     3.  Elastic  layers.     In  the  part  of  the  inner  coat,  at  its  junction  with  the 
middle,  a  layer  of  longitudinal  muscular  fibres  is  represented  as  cut  across,     b,  middle 
coat  with  its  elastic  membranes  ;  c,  outer  coat  with  two  vasa  vasorum. 

The  outer  coat  is  formed  of  connective  tissue  with  a  good  many 
elastic  fibres,  especially  next  to  the  middle  coat.  The  strength  of  an 
artery  depends  largely  upon  this  coat ;  it  is  far  less  easily  cut  or  torn 
than  the  other  coats,  and  it  serves  to  resist  undue  expansion  of  the 


]  10  THE  ESSENTIALS  OF  HISTOLOGY. 

vessel.  Its  outer  limit  is  not  sharply  marked,  for  it  tends  to  blend 
with  the  surrounding  connective  tissue  (hence  it  has  been  termed 
tunica  adventitia). 

Variations  in  structure. — The  aorta  (fig.  135)  differs  in  some  respects  in 
structure  from  an  ordinary  artery.  Its  inner  coat  contains  a  considerable 
thickness  of  sub-epithelial  connective-tissue,  but  the  elastic  layers  of  this  coat 
are  chiefly  composed  of  fine  fibres,  and  are  not  especially  marked  off  from 
those  of  the  middle  coat,  so  that  the  inner  and  middle  coats  appear  almost 
blended  with  one  another.  On  the  other  hand,  there  is  a  very  great  develop- 
ment of  elastic  tissue  in  the  middle  coat,  forming  membranous  layers  which 
alternate  with  layers  of  the  muscular  tissue.  A  good  deal  of  connective 
tissue  also  takes  part  in  the  formation  of  the  middle  coat,  so  that  the  wall  is 
unusually  strong.  The  inner  and  middle  coats  constitute  almost  the  entire 
thickness  of  the  wall,  the  outer  coat  being  relatively  thin. 

The  other  variations  which  occur  in  the  arterial  system  chiefly  have  refer- 
ence to  the  development  and  arrangement  of  the  muscular  tissue.  Thus  in 
many  of  the  larger  arteries  there  are  longitudinal  muscular  fibres  at  the 
inner  boundary  of  the  middle  coat,  and  in  some  arteries  amongst  the  circular 
fibres  of  the  middle  coat.  This  is  the  case  in  the  aorta.  Iri  some  parts  of 
the  umbilical  arteries  there  is  a  complete  layer  of  longitudinal  fibres  internal 
to  the  circular  fibres  and  another  external  to  them,  whilst  the  amount  of 
elastic  tissue  is  very  small.  Longitudinal  fibres  are  also  present  in  some 
other  arteries  (iliac,  superior  meseiiteric,  splenic,  renal,  etc.),  external  to  the 
circular  fibres,  and  therefore  in  the  outer  coat  of  the  artery. 

The  veins  (fig.  136)  on  the  whole  resemble  the  arteries  in  structure, 
but  they  present  certain  differences.  In  the  internal  coat  the  same 


FIG.  136.— TRANSVERSE  SECTION  OF  PART  OF  THE  WALL  OF  ONE  OF  THE  POSTERIOR 
TIBIAL  VEINS  (MAN). 

a,,  epithelial  and  sub-epithelial  layers  of  inner  coat ;  b,  elastic  layers  of  inner  coat;  c,  middle 
coat  consisting  of  irregular  layers  of  muscular  tissue,  alternating  with  connective  tissue, 
and  passing  somewhat  gradually  into  the  outer  connective  tissue  and  elastic  coat,  d. 

layers  may  be  present,  but  the  elastic  tissue  is  less  developed  and 
seldom  takes  the  form  of  a  complete  membrane.  The  endothelium-cells 
are  less  elongated  than  those  of  the  arteries.  The  middle  coat  (c) 
contains  less  elastic  tissue  and  also  less  muscular  tissue,  being  partly 
occupied  by  bundles  of  white  connective-tissue  fibres.  These  are 
derived  from  the  external  coat,  which  is  relatively  better  developed 
in  the  veins  than  in  the  arteries,  so  that,  although  thinner,  their  walls 
are  often  stronger. 

Many  of  the  veins  are  provided  with  valves,  which  are  semilunar  folds 


STRUCTURE  OF  THE  LARGER  BLOOD- VESSELS.  Ill 

of  the  internal  coat  strengthened  by  a  little  fibrous  tissue :  a  few 
muscular  fibres  may  be  found  in  the  valve  near  its  attachment.  The 
layer  of  the  inner  coat  is  rather  thicker,  and  the  endothelium-cells  are 
more  elongated  on  the  side  which  is  subject  to  friction  from  the  current 
of  blood  than  on  that  which  is  turned  towards  the  wall  of  the  vessel. 

The  larger  arteries  and  veins  possess  blood-vessels,  vasa  vaswum,  and 
lymphatics,  both  of  which  ramify  chiefly  in  the  external  coat.  Nerves 
are  distributed  to  the  muscular  tissue  of  the  middle  coat,  after  forming 
a  plexus  in  the  outer  coat. 

Variations  in  different  veins. — The  veins  vary  in  structure  more  than 
do  the  arteries.  In  many  veins  longitudinal  muscular  fibres  are  found  in  the 
inner  part  of  the  middle  coat,  as  in  the  iliac,  femoral,  umbilical,  etc.  ;  in 
others  they  occur  external  to  the  circularly  disposed  fibres,  and  are  described 
as  belonging  to  the  outer  coat.  This  is  the  case  in  the  inferior  vena  cava, 
and  also  in  the  hepatic  veins  and  in  the  portal  vein  and  its  tributaries.  In 
the  superior  and  in  the  upper  part  of  the  inferior  vena  cava  the  circular  fibres 
of  the  middle  coat  are  almost  entirely  absent.  The  veins  of  the  following 
parts  have  no  muscular  tissue,  viz.,  pia  mater,  brain  and  spinal  cord,  retina, 
bones,  and  the  venous  sinuses  of  the  dura  mater  and  placenta. 

It  is  only  the  larger  veins,  and  especially  those  of  the  limbs  that  possess 
valves.  They  are  wanting  in  most  of  the  veins  of  the  viscera  (although 
occurring  abundantly  in  some  of  the  tributaries  of  the  portal  vein),  in  those 
within  the  cranium  and  vertebral  canal,  in  the  veins  of  the  bones,  and  in  the 
umbilical  vein. 


112  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  XXIII, 


SMALLER  BLOOD-  VESSELS.    L YMPHA TIC  SYSTEM. 

1.  TAKE  a  piece  of  pia  mater  which  has  been  stained  with  hasniatoxyliu,  and 
separate  from  it  some  of  the  small  blood-vessels  of  which  it  is  chiefly  com- 
posed. Mount  the  shreds  in  Farrant  or  dilute  glycerine.  The  structure  of 
the  small  arteries  can  be  studied  in  this  preparation,  the  nuclei  of  the  epi- 
thelium and  of  the  muscular  coat  being  brought  distinctly  into  view  by  the 
stain.  The  veins  of  the  pia  mater  possess  no  muscular  tissue.  Capillary 
vessels  which  have  been  dragged  out  from  the  brain  in  removing  the  pia 
mater  may  also  be  seen  in  this  preparation.  Sketch  two  small  arteries  of 
different  sizes,  giving  also  their  measurements. 

2.  Mount  in  Canada  balsam  a  piece  of  the  omentum  of  the  rabbit,  stained 
with  silver  nitrate.    The  membrane  should  be  stretched  over  a  cork  or  a  ring 
of  glass  or  vulcanite,  rinsed  with  distilled  water,  treated  for  five  minutes 
with  1  per  cent,  nitrate  of  silver  solution,  again  washed  and  exposed  to  sun- 
light in  spirit.     When  stained  brown  the  preparation  is  removed  from  the 
light.     Pieces  may  now  be  cut  off  from  the  membrane  and  mounted,  as 
directed,  in  Canada  balsam  ;  they  should  include  one  or  more  blood-vessels. 

This  preparation  is  intended  to  show  the  epithelium  of  the  smaller  blood- 
vessels and  accompanying  lymphatics,  and  also  the  epithelium  of  the  serous 
membrane.  Sketch  a  small  piece  showing  the  epithelium  of  the  vessels. 

3.  Mount  in  Canada  balsam  a  piece  of  the  central  tendon  of  the  rabbit's 
diaphragm    which   has   been   similarly   prepared    (except    that   the   pleural 
surface  has  first  been  brushed  to  remove  the  superficial  epithelium  so  as  to 
enable  the  nitrate  of  silver  more  readily  to  penetrate  to  the  network  of 
lymphatic  vessels  underlying  that  surface).     Observe  the  lymphatic  plexus, 
under  a  low  power  ;  sketch  a  portion  of  the  network.     If  the  peritoneal 
surface  is  fo.cussed,  the  epithelium  which  covers  that  surface  will  be  seen,  and 
opposite  the  clefts  between  the  radially  disposed  tendon-bundles  stomata  may 
be  looked  for  in  this  epithelium. 

4.  Carefully  study  the  circulation  of  the  blood  either  in  the  web  of  the 
frog's  foot  or  in  the  mesentery  or  tongue  of  the  frog  or  toad,  or  in  the  tail  of 
the  tadpole. 


The  coats  of  the  smaller  arteries  and  veins  are  much  simpler  in 
structure  than  those  of  the  larger  vessels,  but  they  contain  at  first  all 
the  same  elements.  Thus  there  is  a  lining  epithelium  (endothelium) 
and  an  elastic  layer  forming  an  inner  coat,  a  middle  coat  of  circularly 
disposed  plain  muscular  tissue,  and  a  thin  outer  coat.  The  same  differ- 
ences also  are  found  between  the  arteries  and  veins,,  the  walls  of  the 
veins  being  thinner  and  containing  far  less  muscular  tissue  (fig.  137), 


SMALLER  BLOOD-VESSELS. 


113 


and  the  lining  epithelium-cells,  much  elongated  in  both  vessels,  are  far 
longer  and  narrower  in  the  small  arteries  than  in  the  corresponding 
veins  (fig.  138). 

In  the  smallest  vessels  it  will  be  found  that  the  elastic  layer  has  dis- 
appeared in  the  veins,  and  the  muscular  tissue  is  considerably  reduced  ^ 
in  thickness  in  both  kinds  of  vessels.  Indeed,  it  is  soon  represented  by 
but  a  single  layer  of  contractile  cells,  and  even  these  no  longer  form  a 
complete  layer.  By  this  time  also,  the  outer  coat  and  the  elastic  layer 
of  the  inner  coat  have  entirely  disappeared  both  from  arteries  and  veins. 
The  vessels  are  reduced,  therefore,  to  the  condition  of  a  tube  formed 
of  pavement-epithelium  cells,  with  a  partial  covering  of  circularly 
disposed  muscular  cells. 

Even  in  the  smallest  vessels,  which  are  not  capillaries,  the  differences 


FlG.  137. — A  SMALL  ARTERY,  A,  WITH  A  CORRESPONDING  VEIN,  B,  TREATED  WITH 

ACETIC  ACID.     (Kolliker.)    (Magnified  350  diameters. ) 

a,  external  coat  with  elongated  nuclei ;  6,  nuclei  of  the  transverse  muscular  tissue  of  the 
middle  coat  (when  seen  endwise,  as  at  the  sides  of  the  vessel,  their  outline  is  circular) ; 
c,  nuclei  of  the  epithelium-cells ;  d,  elastic  layers  of  the  inner  coat. 

between  arteries  and  veins  are  still  manifested.  These  differences  may 
be  enumerated  as  follows  : — The  veins  are  larger  than  the  corresponding 
arteries ;  they  branch  at  less  acute  angles ;  their  muscular  cells  are 
fewer,  and  their  epithelium-cells  less  elongated ;  the  elastic  layer  of  the 
inner  coat  is  always  less  marked,  and  sooner  disappears. 

Capillary  vessels. — When  traced  to  their  smallest  branches,  the 
arteries  and  veins  eventually  are  seen  to  be  continued  into  a  network  of 
the  smallest  blood-vessels  or  capillaries.  The  walls  of  these  are  com- 

H 


114 


THE  ESSENTIALS  OF  HISTOLOGY. 


posed  only  of  flattened  epithelium-cells  (fig.  139)  continuous  with  those 
that  line  the  arteries  and  veins  ;  these  cells  can  be  exhibited  by  staining 
a  tissue  with  nitrate  of  silver.  The  capillaries  vary  somewhat  in  size 
and  in  the  closeness  of  their  meshes ;  their  arrangement  in  different 
parts,  which  is  mainly  determined  by  the  disposition  of  the  tissue- 
elements,  may  best  be  studied  in  injected  preparations,  and  will  be 
described  when  the  structure  of  the  several  organs  is  considered. 


FlG.  138. — A  SMALL  ARTERY,  A,  AND  VEIN,   V,  FROM  THE  SUBCUTANEOUS  CONNECTIVE- 
TISSUE  OF  THE  RAT,  TREATED  WITH  NITRATE  OF  SILVER.      (175  diameters.) 

•i,  a,  endothelial  cells  with  b,  b,  their  nuclei ;  m,  m,  transverse  markings  due  to  staining  of 
substance  between  the  muscular  fibre-cells ;  c,  c,  nuclei  of  connective-tissue  corpuscles 
attached  to  exterior  of  vessel. 

In  the  transparent  parts  of  animals,  the  blood  may  be  seen  flowing 
through  the  capillary  network  from  the  arteries  into  the  veins.     The 


CAPILLARY   BLOOD-VESSELS  AND  LYMPHATICS. 


115 


current  is  very  rapid  in  the  small  arteries,  somewhat  less  so  in  the 
veins,  and  comparatively  slow  in  the  capillaries.  The  current  is  fastest 
in  the  centre  of  the  vessel,  slowest  near  the  wall  (inert  layer),  and 
with  care  it  may  be  observed — especially  where  there  is  any  commen- 
cing inflammation  of  the  part,  as  in  the  mesentery  in  consequence  of 
exposure — that  the  white  blood-corpuscles,  which  always  tend  to 


FIG.  139. — CAPILLARY  VKSSKLS  FROM 
THE  BLADDER  OF  THE  CAT,  MAGNI- 
FIED. 

The  outlines  of  the  cells  are  stained  by 
nitrate  of  silver. 


FIG.  140.— CAPILLARY  BLOOD- 
VESSELS IN  THE  WEB  OF  A 
FROG'S  FOOT,  AS  SEEN  WITH 
THE  MICROSCOPE.  (A.  Thom- 
son.) 

The  arrows  indicate  the  course  of  the 
blood. 


pass  into  the  inert  layer,  and  to  adhere  occasionally  to  the  inner  surface 
of  the  blood-vessels,  here  and  there  pass  through  the  coats  of  the  small 
vessels,  and  appear  as  migratory  cells  in  the  surrounding  connective  tissue. 

LYMPHATIC  SYSTEM. 

To  the  lymphatic  system  belong  not  only  the  lymphatic  vessels  and 
lymphatic  glands,  but  also  the  cavities  of  the  serous  membranes,  which  are 
moistened  with  lymph  and  are  in  open  communication  with  the 
lymphatic  vessels  in  their  parietes. 

The  larger  lymphatic  vessels  somewhat  resemble  the  veins  in  struc- 
ture, except  that  their  coats  are  much  thinner  and  their  valves  much 
more  numerous.  In  lymphatics  of  somewhat  smaller  size,  the  wall  of 
the  vessel  is  formed,  first,  by  a  lining  of  pavement-epithelium  cells 
(lymphatic  endothelium),  which  are  elongated  in  the  direction  of  the 
axis  of  the  vessel ;  and,  secondly,  by  a  layer  of  circularly  and  obliquely 
disposed  muscular  fibres.  In  the  smallest  vessels  (lymphatic  capillaries, 
which,  however,  are  generally  considerably  larger  than  the  blood-capil- 


116 


THE  ESSENTIALS  OF  HISTOLOGY. 


laries),  there  is  nothing  but  the  epithelium  remaining,  and  the  cells  of 
this  are  frequently  not  more  elongated  in  one  direction  than  in  another, 
but  have  a  characteristic  wavy  outline  (fig.  142). 


FIG.  141. — LYMPHATIC  PLEXUS  OF  CENTRAL  TENDON  OF  DIAPHRAGM  OF  RABBIT, 
PLEURAL  SIDE.     (Klein.) 

ft,  larger  vessels  with  lanceolate  cells  and  numerous  valves  ;  b,  c,  lymphatic  capillaries 
with  wavy-bordered  cells. 

Lymphatics  begin  in  two  ways — either  in  the  form  of  plexuses,  as  in 
membranes  (fig.  141),  or  as  lacunar  interstices,  as  is  the  case  in  some  of 
the  viscera. 


LYMPHATIC  VESSELS.  117 

In  order  to  show  the  lymphatic  vessels,  it  is  generally  necessary  to 
stain  a  tissue  with  nitrate  of  silver ;  but  they  may  easily  be  injected  by 
sticking  the  nozzle  of  an  injecting  canula  into  any  tissue  which  contains 
them,  and  forcing  coloured  fluid  under  gentle  pressure  into  the  inter- 
stices of  the  tissue.1 

In  silvered  preparations  it  may  be  observed  that  the  lymphatics 
always  appear  in  the  form  of  clear  channels  in  the  stained  grourid-sub- 


FlG.  142.— A  SMALL  PART  OF  THE  LYMPHATIC  PLEXUS  ON  THE  PLEURAL  SURFACE  OF 

THE  DIAPHRAGM.     (Magnified  110  diameters. )    (Kanvier.) 

L,  lymphatic  vessel  with  characteristic  epithelium  ;  c,  cell-spaces  of  the  connective  tissue 
here  and  there  abutting  against  the  lymphatic. 

stance  of  the  connective  tissue,  and  that  their  walls  are  in  close  con- 
nection with  the  cells  and  cell-spaces  of  that  tissue.  But,  except  in  the 
case  of  the  serous  membranes,  there  is  no  open  communication  between 
the  lymphatic  vessels  and  the  interstices  (areolae)  of  the  connective 
tissue. 

Development  of  the  blood-vessels  and  lymphatics. — The  blood- 
vessels and  lymphatics  are  developed  in  the  connective  tissue  or  in  the 
mesoblastic  tissue  which  precedes  it,  the  first  vessels  being  formed  in 
the  vascular  area  which  surrounds  the  early  embryo.  Both  kinds  of 
vessels  are  developed  from  cells  (vaso-formative  cells  or  angioblasts) 
which  become  hollowed  out  by  an  accumulation  of  fluid  in  their  proto- 
plasm, and  in  the  case  of  developing  blood-vessels  coloured  blood- 

1  For  details  of  procedure  in  injecting  blood-vessels  and  lymphatics  the  student 
is  referred  to  the  author's  Course  of  Practical  Histology. 


118  THE  ESSENTIALS  OF  HISTOLOGY. 

corpuscles  may  also  be  formed  within  these  cells  (see  Development  of 
Blood-corpuscles,  Lesson  II.)  The  cells  branch  and  unite  with  one 
another  to  form  a  network,  and  their  cavities  extend  into  the  branches. 
In  the  meantime  their  nuclei  multiply  and  become  distributed  along 
the  branches,  cell-areas  being  subsequently  marked  out  around  them. 
In  this  way  intercommunicating  vessels— capillaries  containing  blood 
or  lymph — are  produced  (fig.  144).  These  presently  become  connected 
with  previously  formed  vessels,  which  extend  themselves  by  sending 
out  sprouts,  at  first  solid,  and  afterwards  hollowed-out.  It  is  not  pre- 
cisely known  whether  the  larger  blood-vessels  and  lymphatics  are 


FIG.  143. — ISOLATED  CAPILLARY  NETWORK  FORMED  BY  THE  .JUNCTION  OF  SEVERAL 
HOLLOWED-OUT  CELLS,   AND  CONTAINING  COLOURED  BLOOD  CORPUSCLES  IN  A 

CLEAR  FLUID. 

<:,  a  hollow  cell  the  cavity  of  which  does  not  yet  communicate  with  the  network  ;  p,  p,  pointed 
cell-processes,  extending  in  different  directions  for  union  with  neighbouring  capillaries. 

developed  at  first  as  capillaries,  the  muscular  and  other  tissues  being 
subsequently  added,  or  whether  they  are  formed  as  clefts  in  the  meso- 
blastic  tissue  which  become  bounded  by  flattened  cells. 

SKROUS  MEMBRANES. 

The  serous  membranes,  which  may  be  conveniently  studied  in  con- 
nection with  the  lymphatic  sj^stem,  are  delicate  membranes  of  connec- 
tive tissue  which  surround  and  line  the  internal  cavities  of  the  body, 
and  are  reflected  over  many  of  the  thoracic  and  abdominal  viscera  :  in 
passing  to  which  they  form  folds,  within  which  blood-vessels,  lymphatics, 
and  nerves  pass  to  the  viscera. 

The  inner  surface  is  lined  by  a  continuous  layer  of  pai'din-nl- 
epithelium  (serous  endothdium)  (fig.  144),  which  is  very  distinct  in  nitrate 
of  silver  preparations.  In  some  places  there  are  apertures  in  the 
epithelium  which  lead  directly  into  subjacent  lymphatic  vessels.  These 
apertures  are  called  stomata,  and  are  surrounded  by  small  protoplasmic 
cells  (fig.  145  s,  s).  They  are  most  numerous  upon  the  peritoneal  sur- 


SEROUS  AND  SYNOVIAL  MEMBRANES. 


119 


face  of  the  diaphragm,  but  are  present  in  all  serous  membranes,  and 
they  serve  to  prevent  any  undue  accumulation  of  lymph  within  the 


FIG.  144. — ENDOTHELIUM  OF  THE  OMENTUM  OF  THE  RABBIT.    NITRATE  OF  SILVER 
PREPARATION.     (Highly  magnified.) 


FIG.  145. — SMALL  PORTION  OF  PERITONEAL  SURFACE  OF  DIAPHRAGM  OF  RABBIT,  STAINED 
WITH  NITRATE  OF  SILVER  TO  SHOW  THE  SEROUS  EPITHELIUM.     (Klein.) 

/,  lymph-channel  below  the  surface,  lying  between  tendon  bundles,  t,  t,  and  over  which  the 
surface-cells  are  seen  to  be  relatively  smaller,  and  to  exhibit  five  stomata,  s,  s,  leading 
into  the  lymphatic.  The  endothelium  of  the  lymphatic  channel  is  not  represented. 

serous  cavity  during  health.     The  pavement-epithelium  rests  upon  a 
homogeneous  basement-membrane,  which  is  especially  well  marked  in 


120  THE  ESSENTIALS  OF  HISTOLOGY. 

the  serous  membranes  of  man.  The  rest  of  the  thickness  of  the  mem- 
brane is  composed  of  connective  tissue,  with  a  network  of  fine  elastic 
fibres  near  the  inner  surface. 

The  cavities  of  the  serous  membranes  are  originally  formed  in  the 
embryo  as  a  cleft  in  the  mesoblast  (pleuro-peritoneal  split)  which 
becomes  lined  with  epithelium,  and  its  wall  eventually  becomes  differ- 
entiated into  the  serous  membrane. 

SYNOVIAL  MEMBRANES. 

The  synovial  membranes,  which  are  often  compared  with  the  serous 
membranes,  and  are  indeed,  like  the  latter,  connective-tissue  membranes 
which  bound  closed  cavities  moistened  with  fluid,  are  not  so  intimately 
connected  with  the  lymphatic  system,  nor  is  the  fluid  (synovia)  which 
moistens  them  of  the  nature  of  lymph.  Moreover,  there  is  either  no 
epithelial  lining,  or  it  occurs  only  in  patches,  in  place  of  the  continuous 
lining  which  we  find  in  the  serous  membranes.  Curious  villus-like  pro- 
jections occur  in  many  parts ;  they  are  covered  by  small  rounded  cells, 
and  probably  serve  to  extend  the  surface  for  the  secretion  of  synovia. 
The  blood-vessels  of  synovial  membranes  are  numerous,  and  approach 
close  to  the  inner  surface  of  the  membrane. 


LYMPHATIC  GLANDS.  121 


LESSON  XXIV. 

LYMPHATIC  GLANDS,  TONSIL,  THYMUS. 

1.  SECTIONS  of  a  lymphatic  gland  which  has  been  stained  in  bulk  and  em- 
bedded in  paraffin.1  Notice  (1)  the  fibrous  and  muscular  capsule,  with 
trabeculae  extending  inwards  from  it  through  the  cortex  and  anastomosing 
with  one  another  in  the  medulla,  (2)  the  dense  lymphoid  tissue  (adenoid 
tissue  of  some  authors)  forming  large  masses  in  the  cortex  (cortical  nodules) 
and  rounded  cords  in  the  medulla  (medullary  cords).  Notice  also  the  clearer 
channel  or  lymph-sinus  which  everywhere  intervenes  between  the  fibrous 
tissue  and  the  lymphoid  tissue.  Observe  the  fine  fibres  and  branched  cells 
which  bridge  across  this  channel. 

Make  a  general  sketch  under  a  low  power  of  a  portion  of  the  cortex 
together  with  the  adjoining  part  of  the  medulla,  and  under  a  high  power 
drawings  of  small  portions  of  cortex  and  medulla. 

The  retiform  tissue  of  the  lymphatic  glands  has  already  been  studied 
(Lesson  IX.). 

2.  In  sections  of  tonsil  prepared  similarly  to  those  of  the  lymphatic  gland, 
notice  the  large  amount  of  lymphoid  tissue  only  imperfectly  collected  into 
nodules.    Observe  also  that  the  stratified  epithelium,  which  covers  the  mucous 
membrane   here   as   elsewhere   in   the   mouth,    is    infiltrated   with   lymph- 
corpuscles.     Here  and  there  pit-like  recesses  may  be  met  with,  and  glands 
opening  into  the  pits. 

3.  A  similar  preparation  of  the  thymus  gland  of  an  infant.     Notice  that 
the  masses  of  lymphoid  tissue  which  form  the  lobules  of   the  gland   are 
separated  by  septa  of  connective  tissue,  and  that  they  show  a  distinction  into 
two  parts,  cortical  and  medullary.     Observe  the  differences  of  structure  of 
these  two  parts,  and  especially  notice  the  concentric  corpuscles  in  the  medul- 
lary part. 

Make  a  sketch  of  one  of  the  lobules  under  a  low  power  and  of  a  small  part 
of  the  medulla  under  a  high  power,  including  one  or  two  concentric  corpuscles. 
Measure  the  latter. 


Structure  of  a  lymphatic  gland. — A  lymphatic  gland  is  composed 
of  a  fibrous  and  muscular  framework,  which  incloses  and  supports  the 
proper  glandular  substance,  but  is  everywhere  separated  from  it  by  a 
narrow  channel,  bridged  across  by  cells  and  fibres,  which  is  known  as 
the  lymph-channel.  The  framework  consists  of  an  envelope  or  capsule 
(fig.  146,  c),  and  of  trabeculce  (tr\  which  pass  at  intervals  inwards  from 
the  capsule,  and  after  traversing  the  cortex  of  the  gland  divide  and 
reunite  with  one  another  so  as  to  form  a  network  of  fibrous  bands.  At 

1  See  Appendix. 


12-2 


THE  ESSENTIALS  OF  HISTOLOGY. 


one  part  of  the  gland  there  is  usually  a  depression  (hilum),  and  at  the 
bottom  of  this  the  medulla  comes  to  the  surface  and  its  fibrous  bands 
are  directly  continuous  with  the  capsule. 

The  proper  glandular  substance  (l.h)  is  composed  of  lymphoid  tissue, 
i.e.  a  fine  reticulum  with  the  meshes  thickly  occupied  by  lymph- 
corpuscles.  It  occupies  all  the  interstices  of  the  gland,  forming  com- 
paratively large  rounded  masses  in  the  cortex  (lymphoid  nodules,  C) 
between  the  trabeculse,  and  smaller  reticulating  cord-like  masses 
(lymphoid  cords,  M)  in  the  medulla. 


a.l. 


tr. 


FlG.  146.—  DIAGRAMMATIC  SECTION  OF  LYMPHATIC  GLAND.      (Sharpey.) 

a.  1.,  afferent,  e.L,  efferent  lymphatics  ;  C,  cortical  substance;  M,  reticulating  cords  of  medullary 
substance;  l.s,  lymph-sinus;  c,  fibrous  coat  sending  trabeculse,  tr,  into  the  substance  of 
the  gland. 

The  cells  which  bridge  across  the  lymph -channel  in  the  medulla 
(fig.  147,  c)  are  branching  nucleated  cells  which  often  contain  pigment, 
so  that  this  part  of  the  gland  has  a  dark  colour.  The  lymph-channel  is 
bridged  across  not  only  by  these,  but  also  by  fibres  derived  from  the 
capsule  and  trabeculse,  which  pass  to  the  lymphoid  tissue  and  become 
lost  in  its  reticulum.  But  these  fibres  are  often  covered  and  concealed 
by  the  branched  cells. 

Lymphatic  vessels  (fig.  146,  a.L)  enter  the  lymph-channels  after 
passing  through  the  capsule,  and  the  lymph  is  conveyed  slowly  along 
the  channels  of  the  cortical  and  medullary  part  towards  the  hilum, 
taking  up  many  lymph-corpuscles  in  its  passage.  At  the  hilum  it  is 


LYMPHATIC  GLANDS. 


123- 


gathered  up  by  an  efferent  vessel  or  vessels  (e.l.)  which  take  origin  in 
the  lymph-sinuses  of  the  medulla. 

The  efferent  lymphatics  always  contain  many  more  lymph-corpuscles 
than  those  which  enter  the  gland,  for  lymph-corpuscles  are  constantly 
being  formed  by  indirect  division  of  the  pre-existing  cells  in  the 
glandular  substance,  and  especially  in  the  cortical  nodules  (Flemming)r 
and  gradually  find  their  way  into  the  lymph-channel. 


FIG.  147.-  SECTION  OF  THE  MEDULLARY  SUBSTANCE  OF  A  LYMPHATIC  GLAND. 
(300  diameters.)     (Recklinghausen.) 

a,  a,  a,  lyrnphoid  cords  ;  c,  lymph-sinus  ;  b,  b,  trabeculae  ;  d,  d,  capillary  blood-vessels. 

An  artery  passes  into  each  gland  at  the  hilum ;  its  branches  are- 
conveyed  at  first  along  the  fibrous  cords,  but  soon  pass  into  the 
lymphoid  tissue,  where  they  break  up  into  capillaries  (fig.  147,  d). 
The  blood  is  returned  by  small  veins,  which  are  conducted  along  the 
fibrous  trabeculse  to  the  hilum  again. 

In  some  lymphatic  glands  the  fibrous  trabeculae  are  very  slightly 
developed. 

The  tonsils  are  two  masses  of  lymphoid  tissue  placed  one  on  each  side 
of  the  isthmus  of  the  fauces,  into  which  they  project.  They  are  covered 
on  the  free  surface  with  the  stratified  epithelium  of  the  mucous  mem- 
brane, and  this  surface  is  pitted  with  apertures  which  lead  into  recesses- 


124 


THE  ESSENTIALS  OF  HISTOLOGY. 


or  crypts  in  the  substance  of  the  organ  (fig.  148).  These  recesses  are 
all  lined  by  a  prolongation  of  the  stratified  epithelium,  and  into  them 
the  ducts  of  numerous  small  mucous  glands  open.  The  tonsils  are 
composed  almost  entirely  of  lymph  oid  tissue,  which,  besides  being 
diffused  over  the  whole  organ,  is  at  intervals  aggregated  into  small 
nodules,  in  which  the  lymph-cells  are  more  closely  arranged  than  else- 
where. In  these  nodules  active  multiplication  of  the  lymph-cells  by 
karyomitosis  is  constantly  proceeding.  Even  the  epithelium  is  in- 
filtrated with  lymph-corpuscles  (Stohr),  and  they  may  also  wander  out 
on  to  the  free  surface,  and  become  mingled  with  the  saliva  as  salivary 
corpuscles  (see  Lesson  VI.,  §  1). 


FIG.  148. — SECTION  THROUGH  ONE  OF  THE  CRYPTS  OF  THE  TONSIL.    (Stohr.) 

e,  e,  stratified  epithelium  of  surface  of  mucous  membrane,  continued  into  crypt ;  /,  /,  follicles 
or  nodules  of  the  lymphoid  tissue,  which  is  elsewhere  diffuse ;  opposite  each  nodule 
numbers  of  lymph-cells  are  passing  through  the  epithelium  ;  s,  masses  of  cells  which 
have  thus  escaped  from  the  organs  to  mix  with  the  saliva  as  salivary  corpuscles. 

The  mucous  membrane  of  the  neighbouring  part  of  the  pharynx  and 
of  the  back  of  the  tongue  is  similar  in  structure  to  the  tonsils. 

The  thymus  gland  is  a  lymphoid  organ  which  is  found  only  in  the 
embryo  and  during  infancy.  It  is  composed  of  a  number  of  larger  and 
smaller  lobules  (fig.  149),  which  are  separated  from  one  another  by 


THYMUS  GLAND. 


125 


septa  of  connective  tissue,  along  which  the  blood-vessels  and  lymphatics 
pass  to  and  from  the  lobules.  Each  lobule  shows  plainly,  when 
examined  with  the  low  power,  a  distinction  into  an  outer  cortical  and 
an  inner  medullary  portion.  The  cortical  part  of  the  lobule  is  imper- 
fectly divided  into  nodules  by  trabeculse  of  connective  tissue,  and  is 
very  similar  in  structure  to  the  lymphoid  tissue  of  the  lymphatic 
glands  and  tonsils,  with  which  it  also  agrees  in  exhibiting  numerous 
indications  of  indirect  cell-division,  but  the  medulla  is  more  open  in  its 
texture,  and  the  reticulum  is  composed  of  larger,  more  transparent, 
flattened  cells,  and  contains  fewer  lymph-corpuscles.  Moreover,  there 
are  found  in  the  medulla  peculiar  concentrically  striated  bodies  (the 
concentric  corpuscles,  fig.  150),  which  are  "  nests  "  of  flattened  epithelial- 
cells  arranged  concentrically  around  one  or  more  central  cells.  Some- 
times these  corpuscles  are  compound,  two  or  three  being  grouped 
together  and  similarly  inclosed  by  flattened  cells.  The  lymphoid  tissue 
is  abundantly  supplied  with  capillary  blood-vessels,  and  large  lymphatic 
vessels  issue  from  the  organ,  but  in  what  way  the  latter  are  connected 
with  the  lobules  has  not  been  ascertained. 


FlG.  149. — A  LOBULE  OF  THE  THYMUS  OF  A  CHILD,  AS  SEEN  UNDER  A  LOW  POWER. 
c,  cortex  ;  c,  concentric  corpuscles  within  medulla ;  b,  blood-vessels ;  tr,  trabeculse. 

Lymphoid  tissue  occurs  in  many  other  parts  of  the  body  in  addition 
to  the  lymphatic  glands,  tonsils,  and  thymus  gland,  although  it  may 
not,  as  in  these  structures,  constitute  the  bulk  of  the  organ.  Thus  it  is 
found  in  many  mucous  membranes,  such  as  those  of  the  intestine  and 
of  the  respiratory  tract,  both  in  a  diffuse  form  and  also  collected  into 


126 


THE  ESSENTIALS  OF  HISTOLOGY. 


nodular  masses  which  are  like  the  cortical  nodules  of  a  lymphatic 
^gland,  and  may,  like  those,  be  partially  surrounded  by  a  lymph-sinus. 

In  the  spleen  also  a  large  amount  of  lymph- 
oid tissue  is  found  sheathing  the  smaller 
arteries,  and  also  expanded  into  nodular 
masses  (Mcdpighian  corpuscle*  of  the  spleen). 
In  these  organs  it  will  be  studied  subse- 
quently. 

Lymphoid  tissue  also  occurs  in  consider- 
able amount  in  the  serous  membranes, 
especially  in  young  animals  ;  in  the  adult 
it  is  often  transformed  into  adipose  tissue. 
The  tissue  is  generally  developed  in  con- 
nection with  lymphatic  vessels,  an  accumula- 
tion of  retiform  tissue  and  lymph-cells  taking 
place  either  external  to  arid  around  the 

lymphatic  (perili/mphatic  nodule) ;  or  the  lymphatic  is  dilated  into  a 
sinus  and  the  formation  of  lymphoid  tissue  occurs  within  it*1  (endo- 
lympliatic  nodule). 


FIG.  150. — ELEMENTS  OP  THE 
THYMUS.  (300  diameters.) 
(Cadiat.) 

a,  lymph -corpuscles ;  b,  con- 
centric corpuscle. 


THE  SKIN.  127 


LESSON  XXV. 


THE  SKIN. 

1.  SECTIONS  of  skin  from  the  palmar  surface  of  the  fingers.  The  sections  are 
to  be  made  vertical  to  the  surface,  and  should  extend  down  as  far  as  the  sub- 
cutaneous tissue.  They  may  be  stained  with  hsematoxylin  or  picro-carmine 
and  mounted  in  Canada  balsam.  In  these  sections  notice  the  layers  of  the 
epidermis  and  their  different  behaviour  to  the  staining  fluid.  Notice  also  the 
papillae  projecting  from  the  corium  into  the  epidermis,  and  look  for  tactile 
corpuscles  within  them.  In  very  thin  parts  of  the  sections  the  fine  inter- 
cellular channels  in  the  deeper  parts  of  the  epithelium  (see  Lesson  VI.  p.  27) 
may  be  seen  with  a  high  power.  The  convoluted  tubes  of  the  sweat-glands 
will  be  seen  here  and  there  in  the  deeper  parts  of  the  corium,  and  in  thick 
sections  the  corkscrew-like  channels  by  which  the  sweat  is  conducted  through 
the  epidermis  may  also  be  observed.  Make  a  sketch  showing  the  general 
structure  under  a  low  power,  and  other  sketches  to  exhibit  the  most  important 
details  under  a  high  power.  Measure  the  thickness  of  the  epidermis  and  the 
length  of  the  papillse. 

2.  Sections  of  the  skin  of  the  scalp,  vertical  to  the  surface  and  parallel  to 
the  slope  of  the  hair-follicles,  and  others  parallel  to  the  surface,  and  therefore 
across  the  hair  follicles.     Stain  and  mount  in  the  same  way  as  in  the  last 
preparation.     Examine  also  the  structure  of  the  hairs. 

In  these  preparations  the  details  of  structure  of  the  hairs  and  hair-follicles 
together  with  the  sebaceous  glands  and  the  little  muscles  of  the  hair-follicles 
are  to  be  made  out. 

3.  Vertical  sections  across  the  nail  and  nail-bed,  ciit  with  a  strong  razor. 
To  cut  such  hard  structures  as  the  nail  it  is  best  to  soak  the  tissue  in  strong 
gurn  arabic  for  a  few  days,  then  place  it  in  an  appropriate  position  upon  a  cork 
or  on  the  object-carrier  of  a  microtome,  and  plunge  the  whole  into  70  per 
cent,  alcohol.     This  renders  the  gum  hard,  and  enables  sections  to  be  cut  of 
sufficient  fineness.     To  remove  the  gum  the  sections  are  placed  in  water  for  a 
few  hours  ;  they  may  then  be  stained  with  hematoxylin  or  picro-carmine  and 
mounted  in  the  usual  manner  in  Canada  balsam.     Notice  the  ridges  (not 
papillae)  of   the  coriuin  projecting  into  the  epidermis.      Observe  also  the 
distinction  of  the  epidermis  into  Malpighian  layer  and  nail  proper. 

4.  Mount  in  Canada  balsam  a  section  from  a  portion  of  skin  of  which  the 
blood-vessels  have  been  injected,  and  notice  the  distribution  of  the  capillaries 
to  the  sweat-glands,  to  the  hair-follicles,  and  to  the  papillary  surface  of  the 
corium. 


The  skin  is  composed  of  two  parts,  epidermis  and  cutis  vera. 

The  epidermis,  or  scarf  skin,  is  a  stratified  epithelium  (fig.  151).  It 
is  composed  of  a  number  of  layers  of  cells,  the  deeper  of  which  are  soft 
and  protoplasmic,  and  form  the  rete  mucosum  of  Malpighi,  whilst  the 


128 


THE  ESSENTIALS  OF  HISTOLOGY. 


superficial  layers  are  hard  and  horny,  this  horny  portion  sometimes 
constituting  the  greater  part  of  the  thickness  of  the  epidermis.  The 
deepest  cells  of  the  rete  mucosum,  which  are  set  on  the  surface  of  the 
cutis  vera,  are  columnar  (fig.  151,  c)  in  shape.  In  the  coloured  races 
of  mankind  these  cells  contain  pigment-granules.  In  the  layers 
immediately  above  them  the  cells  are  polyhedral  (fig.  151,  p}. 
Between  all  these  cells  of  the  rete  mucosum  there  are  fine  intercellular 
clefts  which  separate  the  cells  from  one  another,  but  are  bridged  across 
by  fine  fibres,  which  pass  from  cell  to  cell,  and  also  through  the  sub- 
stance of  the  cells  (Eanvier,  Delepine).  The  intercellular  channels 
serve  for  the  passage  of  lymph,  and  within  them  occasionally  lymph- 
corpuscles  may  be  found,  often  having  a  stellate  figure  from  compression. 


FIG.  151.— SECTION  OF  EPIDERMIS.    (Ranvier.) 

H,  horny  layer,  consisting  of  s,  superficial  horny  scales  ;  sw,  swollen-out  horny  cells  ;  s.l., 
stratum  lucidum  ;  M,  rete  mucosum  or  Malpighian  layer,  consisting  of  p,  prickle-cells, 
several  rows  deep ;  c,  elongated  cells  forming  a  single  stratum  near  the  corium ;  and 
s.gr,  stratum  granulosum  of  Langerhans,  just  below  the  stratum  lucidum  ;  n,  part  of  a 
plexus  of  nerve-fibres  in  the  superficial  layer  of  the  cutis  vera.  From  this  plexus  fine 
varicose  nerve-fibrils  may  be  traced  passing  up  between  the  epithelium-cells  of  the 
Malpighian  layer. 

The  most  superficial  layer  of  the  rete  mucosum  is  formed  of  some- 
what flattened  granular-looking  cells  (stratum  granulosum,  fig.  151,  s.gr  ; 
fig.  152,  c}.  Immediately  above  this  layer,  the  liwny  part  of  the 


THE  SKIN. 


129 


epidermis  commences,  as  a  layer  of  clear  compressed  cells  several  deep 
(stratum  lutidum,  s.L).  Above  this  comes  the  main  part  of  the  horny 
layer.  It  is  composed  of  a  number  of  layers  of  somewhat  swollen  cells 
(epitrichial  stratum,  sw),  the  nuclei  of  which  are  no  longer  visible. 
These  cells  are  replaced  near  the  surface  by  thin  horny  scales 
(stratum  squamosum),  which  eventually  become  detached  (s).  The 
epitrichial  stratum  is  only  found  in  certain  parts  which  have  a  thick 
epidermis  and  are  not  covered  with  hair  (e.g.  the  palms  and  soles). 
In  the  embryo  it  covers  the  whole  body,  but  is  thrown  oft'  when  the 
hairs  are  developed. 

The  growth  of  the  epidermis  takes  place  by  a  multiplication  of  the 
cells  of  the  deepest  layer.  The  newly  formed  cells,  as  they  grow,  push 
towards  the  surface  those  which  were  previously  formed,  and  in  their 
progress  the  latter  undergo  a  chemical  transformation,  which  converts 
their  protoplasm  into  horny  material :  this  change  seems  to  occur  just 
above  the  stratum  granulosum  (see  fig.  152).  The  granules  which 
occupy  the  cells  of  the  last-mentioned  layer  are  composed  of  a  substance 
termed  eleidin,  which  according  to  Ranvier  is  transformed  into  keratin. 

No  blood-vessels  pass  into  the  epidermis,  but  it  receives  nerves 
which  ramify  between  the  cells  of  the  rete  mucosum  in  the  form  of 
fine  varicose  fibrils  (fig.  151). 


FlG.  152. — POKTION  OF  EPIDERMIS  FROM  A  SECTION  OF  THE  SKIN  OF  THE  FINGER, 

COLOURED  WITH  PICROCARMINATE  OF  AMMONIA.      (Ranvier. ) 

a,  stratum  corneum  ;  b,  stratum  lucidum  with  diffused  flakes  of  eleidin  ;  c,  stratum  granu- 
losum, the  cells  filled  with  drops  of  eleidin ;  d,  prickle-cells  ;  e,  dentate  projections  by 
which  the  deepest  cells  of  the  epidermis  are  fixed  to  the  cutis  vera. 

The  cutis  vera  or  corium  is  composed  of  dense  connective-tissue, 
which  becomes  more  open  and  reticular  in  its  texture  in  its  deeper 
part,  where  it  merges  into  the  subcutaneous  tissue.  It  is  thickest  over 
the  posterior  aspect  of  the  trunk,  whereas  the  epidermis  is  thickest  on 

I 


130  THE  ESSENTIALS  OF  HISTOLOGY. 

the  palms  of  the  hands  and  soles  of  the  feet.  The  superficial  or 
vascular  layer  of  the  corium  bears  minute  papillce,  which  project  up 
into  the  epidermis,  which  is  moulded  over  them.  These  papillae  for 
the  most  part  contain  looped  capillary  vessels  (fig.  153),  but  some, 
especially  those  of  the  palmar  surface  of  the  hand  and  fingers,  and  the 
corresponding  part  of  the  foot,  contain  tactile  corpuscles,  to  which 
medullated  nerve-fibres  pass  (fig.  114,  b,  p.  99). 


FIG.  153. — DUCT  OF  A  SWEAT-GLAND  PASSING  THROUGH  THE  EPIDERMIS. 
(Magnified  200  diameters.)    (Heitzmann.) 

BP,  papillae  with  blood-vessels  injected  ;   V,  rete  mucosum  between  the  papillae  ;  E,  stratum 
corneum  ;  PL,  stratum  granulosum  ;  D,  duct,  opening  on  the  surface  at  p. 

In  some  parts  of  the  body  (scrotum,  penis,  nipple,  and  its  areola), 
involuntary  muscular  tissue  occurs  in  the  deeper  portions  of  the  cutis 
vera,  and  in  addition,  wherever  hairs  occur,  small  bundles  of  this  tissue 
are  attached  to  the  hair-follicles. 

The  blood-vessels  of  the  skin  are  distributed  almost  entirely  to  the 
surface,  where  they  form  a  close  capillary  network,  sending  up  loops 
into  the  papillae  (fig.  153).  Special  branches  are  also  distributed  to  the 
various  appendages  of  the  skin,  viz.  the  sweat-glands  and  hair-follicles, 
with  their  sebaceous  glands  and  little  muscles,  as  well  as  to  the  little 
masses  of  adipose  tissue  which  may  be  found  in  the  deeper  parts  of  the 
cutis. 

The  lymphatics  originate  near  the  surface  in  a  network  of  vessels, 
which  is  placed  a  little  deeper  than  the  blood-capillary  network.  They 
receive  branches  from  the  papillae,  and  pass  into  larger  vessels,  which 
are  valved,  and  which  run  in  the  deeper  or  reticular  part  of  the  corium. 


THE  SKIN. 


131 


rhich 


From  these  the  lymph  is  carried  away  by  still  larger  vessels, 
course  in  the  subcutaneous  tissue. 

The  appendages  of  the  skin  are  the  nails,  the  hairs,  with  their 
sebaceous  glands  and  the  sweat-glands.  They  are  all  developed  as 
thickenings  and  downgrowths  of  the  Malpighian  layer  of  the  epidermis. 


FIG.  154. --SECTION  ACROSS  THE  NAIL  AND  NAIL-BED.     (100  diameters. )    (Heitzmann.) 
P.  ridges  with  blood-vessels  ;  £,  rete  mucosum  ;  N,  nail. 

The  nails  are  thickenings  of  the  stratum  lucidum  of  the  epidermis, 
which  are  developed  over  a  specially  modified  portion  of  the  corium, 

(which  is  known  as  the  bed  or  matrix  of  the  nail,  the  depression  at  the 
posterior  part  of  the  nail-bed  from  which  the  root  of  the  nail  grows 
being  known  as  the  nail-groove.  The  distal  part  of  the  nail  forms  the 
free  border,  and  is  the  thickest  part  of  the  body  of  the  nail.  The  horny 
substance  of  the  nail  (fig.  154,  N)  is  composed  of  clear  horny  cells, 
each  containing  the  remains  of  a  nucleus ;  it  rests  immediately  upon 
a  Malpighian  layer  (B)  similar  to  that  which  is  found  in  the  epidermis 
generally.  The  corium  of  the  nail-bed  is  beset  with  longitudinal 
ridges  instead  of  the  papillae  which  are  present  over  the  rest  of  the 
skin;  these,  like  the  rest  of  the  superficial  part  of  the  corium,  are 
extremely  vascular.  The  nails  are  developed  in  the  fo3tus  at  about 
the  third  month,  the  groove  being  formed  at  this  time  in  the  corium, 
and  the  nail-rudiment  appearing  in  it  as  a  thickening  of  the  stratum 
lucidum,  which  lies  over  the  bed.  It  becomes  free  in  the  sixth  month, 


132  THE  ESSENTIALS  OF  HISTOLOGY. 

its  free  end  being  at  first  thin,  but  as  it  grows  forward  over  the  bed  it 
appears  to  receive  additions  on  its  under  surface  —  at  least  in  the  pos- 
terior part  of  the  bed  —  so  that  after  a  time  the  distal  end  becomes 
thicker.  The  epitrichial  layer  of  the  cuticle  which  originally  covered 
the  developing  nail  becomes  detached  about  the  fifth  month,  and,  after 
birth,  only  remains  as  the  narrow  border  of  cuticle  which  overlies  the 


The  hairs  are  growths  of  the  epidermis,  developed  in  little  pits  — 
the  hair-follicles  —  which  extend  downwards  into  the  deeper  part  of  the 
jcorium,  or  even  into  the  subcutaneous  tissue.  The  hair  grows  from 
the  bottom  of  the  follicle,  the  part  which  thus  lies  within  the  follicle 
being  known  as  the  root  (fig.  156). 

The  substance  of  a  hair  is  mainly  composed  of  a  pigmented,  horny, 
fibrous  material  (fig.  155,  /),  which  can  be  separated  by  the  action  of 
sulphuric  acid  into  long  tapering  fibrillated  cells,  the  nuclei  of  which 
are  still  visible.  This  fibrous  substance  of  the  hair  is  covered  by  a  layer 
of  delicate  imbricated  scales  termed  the  hair-cuticle  (c).  In  many  hairs, 
but  not  in  all,  the  centre  is  occupied  by  a  dark-looking  axial  substance 
(medulla,  m),  formed  of  angular  cells  which  contain  granules  of  eleidin, 
and  frequently  have  a  dark  appearance  from  the  presence  of  minute 
air-bubbles.  The  latter  may  also  occur  in  interstices  in  the  fibrous  sub- 
stance. When  they  are  present,  the  hair  looks  white  by  reflected  light. 
The  root  has  the  same  structure  as  the  body  of  the  hair,  except  at  its 
extremity,  which  is  enlarged  into  a  knob  (fig.  156,  6);  this  is  composed 
mainly  of  soft,  growing  cells,  and  fits  over  a  vascular  papilla  (p\  which 
projects  up  into  the  bottom  of  the  follicle.  The  follicle,  like  the  skin 
itself,  of  which  it  is  a  recess,  is  composed  of  two  parts  :  one  epithelial, 
and  the  other  connective  tissue.  The  epithelial  or  epidermic  part  of 
the  follicle  closely  invests  the  hair-root,  and  is  often  in  great  part 
dragged  out  with  it  ;  hence  it  is  known  as  the  root-sheath.  It  consists 
of  an  outer  layer  of  soft  columnar  and  polyhedral  cells,  like  the  Mal- 
pighian  layer  of  the  epidermis  —  the  outer  root-sheath  (figs.  156,  /; 
157,  e)',  and  of  an  inner,  thinner,  horny  stratum  next  the  hair  —  the 
inner  root-sheath  (figs.  156,  g\  157,  /).  The  inner  root-sheath  itself 
consists  of  three  layers,  the  outermost  being  composed  of  oblong  cells 
without  nuclei  (Henle's  layer),  the  next  of  flattened  polyhedral  nucleated 
cells  (Huxley's  layer],  and  the  third  —  the  cuticle  of  the  'root-sheath  —  being 
a  thin  layer  of  downwardly  imbricated  scales,  which  fit  over  the 
upwardly  imbricated  scales  of  the  hair  itself. 

The  connective  tissue  or  dermic  part  of  the  hair  follicle  (fig.  157, 
a,  c,  d)  is  composed  internally  of  a  vascular  layer,  separated  from  the 
root-sheath  by  a  basement-membrane  termed  the  hyaline  layer  of  the 


THE  SKIN.  133 

follicle.     This  inner  vascular  layer  corresponds  to  the  superficial  layer 


FIG.    155.— PIECE    OF    HUMAN 
HAIR.     (Magnified.) 

A,  seen  from  the  surface ;  B,  in 
optical  section,  c,  cuticle ;  /, 
fibrous  substance ;  m,  medulla, 
the  air  having  been  expelled  by 
Canada  balsam. 


FIG.  157. — SECTION  OF  HAIR- 
FOLLICLE.     (Biesiadecki.) 

1,  dermic  coat  of  follicle  ;  2,  epi- 
dermic coat  or  root-sheath,  a, 
outer  layer  of  dermic  coat,  with 
blood-vessels,  6,  6,  cut  across;  c, 
middle  layer;  d,  inner  or  hyaline 
layer ;  e,  outer  root-sheath  ;  /,  g, 
inner  root-sheath  ;  h,  cuticle  of 
root-sheath;  I,  hair. 


FIG.  156. — HAIR-FOLLICLE  IN  LONGITUDINAL 
SECTION.     (Biesiadecki.) 

».,  mouth  of  follicle ;  b,  neck  ;  c,  bulb ;  d,  e,  dermic 
coat;/,  outer  root-sheath;  g,  inner  root-sheath; 
h,  hair ;  k,  its  medulla ;  I,  hair-knob ;  m,  adipose 
tissue ;  n,  hair-muscle ;  o,  papilla  of  skin ;  p, 
papilla  of  hair ;  s,  rete  mucosum,  continuous  with 
outer  root-sheath ;  ep,  horny  layer ;  t,  sebaceous 
gland. 


134 


THE  ESSENTIALS  OF  HISTOLOGY. 


of  the  cutis  vera.  Its  fibres  and  cells  have  a  regular  circular  arrange- 
ment around  the  follicle,  the  cells  being  flattened  against  the  hyaline 
layer.  Externally  the  dermic  coat  of  the  follicle  has  a  more  open 
texture,  corresponding  to  the  reticular  part  of  the  cutis,  and  containing 
the  larger  branches  of  the  arteries  and  veins.  In  the  large  tactile 
hairs  of  animals,  the  veins  near  the  bottom  of  the  follicle  are  dilated 
into  sinuses,  so  as  to  produce  a  kind  of  erectile  structure. 


FIG.  158.— LONGITUDINAL  SECTION  THROUGH  THE  FOLLICLE  OF  A  HAIR  WHICH  HAS. 
CEASED  TO  GROW.     (Ranvier.) 

m,  epithelium  at  the  bottom  of  the  follicle  (which  contains  no  papilla) ;  I,  modified  hair-bulb  ; 
c,  neck  of  the  follicle  ;  s,  sebaceous  gland  ;  o,  epithelial  projection  at  the  insertion  of  the 
arrector  pili. 

The  hair  grows  from  the  bottom  of  the  follicle  by  multiplication  of 
the  soft  cells  which  cover  the  papilla,  these  cells  becoming  elongated  to 
form  the  fibres  of  the  fibrous  substance,  and  otherwise  modified  to  pro- 
duce the  medulla  and  cuticle. 

When  a  hair  is  eradicated,  a  new  hair  is  produced  from  these  cells. 
It  is  not  uncommon  to  find  hair-follicles  in  which  the  whole  of  the  lower 
part  has  degenerated  in  such  a  way  that  the  vascular  papilla,  and  the 
soft,  growing  cells  which  cover  it,  may  have  entirely  disappeared,  the 


THE  SKIN. 


135 


hair-bulb  being  now  attached  at  its  sides  as  well  as  below  to  the 
epithelium  of  the  follicle  (fig.  158).  The  hair  then  ceases  to  grow,  and 
eventually  becomes  lost,  but  its  place  may  be  again  supplied  by  a  new 
hair,  which  becomes  formed  in  a  downgrowth  from  either  the  bottom  or 
the  side  of  the  hair-follicle,  a  new  papilla  first  becoming  formed  at  the 


FIG.  159.— REPLACEMENT  OF  OLD  HAIR  BY  A  NEWLY-DEVELOPING  ONE  IN 
THE  HUMAN  SCALP.     (Ranvier.) 

p,  papilla  of  the  new  hair ;  i,  its  inner  root-sheath ;  e,  its  outer  root-sheath  ; 
p',  attached  lower  extremity  of  the  old  hair ;  r,  epithelial 


insertion  of  arrector  pili, 


projection  at 


extremity  of  the  downgrowth  (fig.  159).  If  not  previously  detached, 
the  old  hair  may  be  pushed  from  out  the  follicle  by  the  one  which 
replaces  it. 

The  hairs  are  originally  developed  in  the  embryo  in  the  form  of 
small  solid  downgrowths  from  the  Malpighian  layer  of  the  epidermis 
(fig.  160).  The  hair-rudiment,  as  it  is  called,  is  at  first  composed 
entirely  of  soft,  growing  cells  ;  but  presently  those  in  the  centre  become 
differentiated,  so  as  to  produce  a  minute  hair  invested  by  inner  root- 
sheath,  and  its  base  resting  upon  a  papilla  which  has  grown  up  into 
the  extremity  of  the  hair-rudiment  from  the  corium  (fig.  161  p).  As 


136 


THE  ESSENTIALS  OF  HISTOLOGY. 


the  minute  hair  grows,  it  pushes  its  way  through  the  layers  of  the 
epidermis,  which  it  finally  perforates,  the  epitrichial  layer  being  thrown 
off  (p.  129).  The  hair-rudiments  commence  at  the  third  or  fourth 
month  of  fostal  life  ;  their  growth  is  completed  about  the  fifth  or  sixth 
month,  and  they  form  a  complete  hairy  covering  termed  the  lanugo. 


FIG.  160.  —  HAIR-RUDIMENT  FROM  AN 
EMBRYO  OF  six  WEEKS.    (Kolliker.) 
a,  horny,  and  6,  mucous  or  Malpighian 
layer  of  cuticle  ;  i,  basement-mem- 
brane ;  in,  cells,  some  of  which  are 
assuming  an  oblong  figure,  which 
chiefly  form  the  future  hair. 


FIG.  161.— DEVELOPING  HAIR  FROM 

HUMAN  EMBRYO  OF  4i  MONTHS. 

(Ranvier.) 

p,  papilla ;  /,  hair-rudiment ;  i,  cells 
forming  inner  root-sheath  ;  k,  kera- 
tinised  part  of  inner  root-sheath, 
uncoloured  by  carmine ;  e,  outer 
root-sheath ;  b,  epithelial  projection 
for  insertion  of  arrector  pili  ;  s, 
sebaceotis  gland  ;  t,  sebaceous 
matter  forming  independently  in 
the  part  which  will  become  the 
neck  of  the  follicle. 

This  is  entirely  shed  within  a  few  months  of  birth,  the  new  hairs  being 
formed  in  downgrowths  from  the  old  hair-follicles  in  the  manner  already 
mentioned. 

Hairs  grow  at  the  rate  of  half  an  inch  per  month.  They  are  found 
all  over  the  body  except  on  the  palms  of  the  hands  and  the  soles  of  the 
feet,  and  on  the  distal  phalanges  of  the  fingers  and  toes.  They  usually 


THE  SKIN.  137 

slant,  and  in  the  negro  the  hair-follicles  are  even  considerably  curved. 
On  the  scalp  they  are  set  in  groups,  as  is  well  seen  in  a  horizontal 
section. 

The  hairs  of  animals  are  often  curiously  marked  by  the  arrangement 
of  their  medulla,  the  markings  being  characteristic  of  particular 
species. 

Muscles  of  the  hairs. — A  small  muscle  composed  of  bundles  of  plain 
muscular  tissue  is  attached  to  each  hair-follicle  (arrector  pili,  fig.  156,  n) ; 
it  passes  from  the  superficial  part  of  the  corium,  on  the  side  to  which 
the  hair  slopes,  obliquely  downwards,  to  be  attached  near  the  bottom 
of  the  follicle  to  a  projection  formed  by  a  localised  hypertrophy  of  the 
outer  root-sheath.  When  the  muscle  contracts,  the  hair  becomes 
erected,  and  the  follicle  is  dragged  upwards  so  as  to  cause  a  prominence 
on  the  general  surface  of  the  skin,  whilst  the  part  of  the  corium  from 
which  the  little  muscle  arises  is  correspondingly  depressed ;  the 
roughened  condition  known  as  '  goose  skin '  being  in  this  way  pro- 
duced. 

The  sebaceous  glands  (fig.  156,  t)  are  small  saccular  glands,  the 
ducts  from  which  open  into  the  mouths  of  the  hair-follicles.  Both  the 
duct  and  the  saccules  are  lined  by  epithelium,  which  becomes  charged 
with  fatty  matter.  This  sebaceous  matter  is  discharged  into  the  cavity 
of  the  saccule,  probably  owing  to  the  disintegration  of  the  cells  within 
which  it  is  formed.  There  may  be  two  or  more  sebaceous  glands 
attached  to  each  follicle. 

The  sebaceous  glands  are  developed  as  outgrowths  from  the  outer 
root-sheath  (fig.  161,  s). 

The  sweat-glands  are  abundant  over  the  whole  skin,  but  they  are 
most  numerous  on  the  palm  of  the  hand  and  on  the  sole  of  the  foot. 
They  are  composed  of  coiled  tubes,  which  lie  in  the  deeper  part  of  the 
integument  and  send  their  ducts  up  through  the  cutis  to  open  on  the 
surface  by  corkscrew-like  channels  which  pierce  the  epidermis  (fig.  153, 
p.  130). 

The  glandular  or  secreting  tube  is  a  convoluted  tube  composed  of  a 
basement-membrane  lined  by  a  single  layer  of  cubical  or  columnar 
epithelium-cells,  and  with  a  layer  of  longitudinally  or  obliquely 
disposed  fibres  between  the  epithelium  and  basement-membrane.  These 
fibres  are  usually  regarded  as  muscular,  but  the  evidence  on  this  point  is 
not  conclusive.  The  secreting  tube  is  considerably  larger  than  the  efferent 
tube  or  duct,  which  begins  within  the  gland  and  usually  makes  several 
convolutions  before  leaving  the  gland  to  traverse  the  cutis  vera.  The 
efferent  tube  has  an  epithelium  consisting  of  two  or  three  layers  of 
cells,  within  which  is  a  well-marked  cuticular  lining,  but  there  is  no 


138 


THE  ESSENTIALS  OF  HISTOLOGY. 


muscular  layer.  The  passage  through  the  epidermis  has  no  proper 
wall,  but  is  merely  a  channel  excavated  between  the  epithelium-cells. 

The  ceruminous  glands  of  the  ear  are  modified  sweat-glands. 

The  sweat-glands  are  developed,  like  the  hairs,  from  downgrowths  of 
the  Malpighian  layer  of  the  epidermis  into  the  corium,  the  rudiments 


FIG.  162. — SECTION  OF  A  SWEAT-GLAND  IN  THE  SKIN  OF  MAX. 

a,  a,  secreting  tube  in  section  ;  6,  a  coil  seen  from  above  ;  c,  c,  efferent  tube  ;  d,  intertubular 
connective  tissue  with  blood-vessels.  1,  basement  membrane ;  2.  muscular  fibres  cut 
across  ;  3,  secreting  epithelium  of  tubule. 

which  are  thus  formed  becoming  eventually  coiled  up  at  their  extremi- 
ties and  converted  into  hollow  tubes.  The  (muscular)  fibres  of  the 
tubes  as  well  as  the  secreting  epithelium-cells  are  thus  epiblastic 
structures. 

The  sweat-glands  receive  nerve-fibres,  and  each  gland  has  a  special 
cluster  of  capillary  blood-vessels. 


STKUCTUKE  OF  THE  HEART.  13<> 


LESSON   XXVI. 


STRUCTURE  OF  THE  HEART. 

1.  IN  a  section  through  the  wall  of  the  auricle,  stained  with  magenta  and 
mounted  in  dilute  glycerine,  or  stained  with  hsematoxylin  and  mounted  in 
Canada  balsam,  notice  the  relative  thickness  of  the  epicardium,  myocardium, 
and  endocardium.  Observe  the  blood-vessels  and  nerve-fibres  under  the 
epicardium,  often  embedded  in  fat ;  here  and  there  a  ganglion  may  be  seen 
under  this  membrane.  Notice  also  the  elastic  networks  under  both  the 
pericardium  and  endocardium.  Make  a  general  sketch  from  this  section. 

2.  Section  through  the  wall  of  the  ventricle,  stained  with  hsematoxylin  and 
mounted  in  Canada  balsam.     The   muscular  fibres   are  variously  cut.     In 
those  cut  longitudinally,  notice  the  branching  of  the  fibres  and  their  union 
into  a  network.     Notice  also  that  although  the  fibres  are  cross-striated  this 
is  less  distinct  than  in  voluntary  muscle,  and  the  nuclei  lie  in  the  centre  of 
each  fibre.     Transverse  markings  may  also  be  seen  passing  across  the  fibres 
between  the  nuclei  and  indicating  a  division  into  cells.     The  endocardium  is 
very  thin,  especially  over  the  columnae  cariiese. 

3.  If  a  portion  of  endocardium  of  the  sheep's  heart  is  spread  out  oil  a  slide 
and  examined  in  salt  solution,  a  network  of  large  beaded  fibres  may  be  seen 
with  a  low  power  or  even  with  a  lens.     These  are  the  fibres  of  Purkinje,  and 
they  will  be  seen  to  be  formed  of  large,  square-looking  cells,  usually  contain- 
ing two  nuclei,  and  having  striated  muscular  substance  at  their  periphery. 

4.  The  lymphatics  of  the  heart  are  easily  injected  with  Berlin  blue  by 
sticking  the  nozzle  of  the  injecting  syringe  into  the  muscular  substance,  in 
the  interstices  of  which  the  lymphatics  arise.    These  commencing  lymphatics 
lead  to  efferent  vessels  which  pass  to  the  base  of  the  heart  under  the  epi- 
cardium. 

5.  Section  through  one  of  the  valves  of  the  heart,  stained  and  mounted  as 
in  preparation  2.1 

6.  The  epithelium  which  covers  the  epicardium,  and  that  which  lines  the 
endocardium,  may  be  studied  in  preparations  of  the  fresh  organ  which  have 
been  well  washed  with  distilled  water  ;  then  treated  with  nitrate  of  silver 
and  subsequently  exposed  to  the  light  and  hardened  in  alcohol. 


The  muscular  tissue  of  the  heart  (myocardium)  forms  the  main 
thickness  of  the  ventricles  and  also  of  parts  of  the  auricles.  It  is 
composed  of  a  network  of  fibres  which  are  formed  of  uninucleated 

1  The  appearances  which  are  to  be  studied  in  sections  1,  2,  and  5  can  all  be  obtained  in 
one  preparation,  viz.  a  vertical  section  including  a  portion  of  auricle  and  ventricle  and 
a  flap  of  the  intervening  auriculo-ventricular  valve. 


140 


THE  ESSENTIALS  OF  HISTOLOGY. 


transversely  striated  cells,  the   structure  of  which  has  already  been 
studied  (Lesson  XVIL,  p.  81). 


FIG.  163,  A. — SECTION  OF  THE  EPICAEDIUM  OF  THE  RIGHT  AURICLE. 
c.,  serous  epithelium  in  section  ;  6,  connective-tissue  layer ;  c,  elastic  network  ;  d,  subserous 
areolar  tissue  ;  e,  fat ;  /',  section  of  a  blood-vessel ;  g,  a  small  ganglion  ;  ht  muscular  fibres 
of  the  myocardium  ;  i,  intermuscular  areolar  tissue. 

B. — SECTION  OF  THE  ENDOCARDIUM  OF  THE  RIGHT  AURICLE. 

c,  lining  epithelium  ;  6,  connective-tissue  with  fine  elastic  fibres  ;  c,  layer  with  coarser  elastic 
fibres  ;  d,  sub-endocardial  connective  tissue  continuous  with  the  intermuscular  tissue  of 
the  myocardium  ;  h,  muscular  fibres  of  the  myocardium  ;  m,  plain  muscular  tissue  in  the 
endocardium. 


FIG.  164. — FRAGMENT  OF  THE  NETWORK  OF  PURKINJE  FROM  THE  VENTRICULAR 

ENDOCARDIUM  OF  THE  SHEEP.      (Ranvier.)     £-«£. 
c,  cell ;  n,  nuclei ;  /,  peripheral  striated  substance. 

Iii  the  interstices  of  the  muscular  tissue  there  is  a  little  areolar  tissue 
in  which  run  the  very  numerous  blood-capillaries  and  the  lacunar 
lymphatics. 


STRUCTURE  OF  THE  HEART. 


141 


The  myocardium  is  covered  externally  by  a  layer  of  serous  membrane 
— the  epicardium  (cardiac  pericardium,  fig.  163,  A) — composed,  like 
other  serous  membranes,  of  connective  tissue  and  elastic  fibres,  the 
latter  being  most  numerous  in  its  deeper  parts.  Underneath  the 
epicardium  run  the  blood-vessels,  nerves,  and  lymphatic  vessels  of  the 
heart,  embedded  in  areolar  and  adipose  tissue,  this  tissue  being  con- 
tinuous with  that  which  lies  between  the  muscular  bundles ;  and  the 
free  surface  of  the  membrane  is  covered  by  serous  endothelium. 


FIG.  165.— SECTION  THROUGH  ONE  OF  THE  FLAPS  OF  THE  AORTIC  VALVE,  AND  PART  OF 
THE  CORRESPONDING  SINUS  OF  VALSALVA,  WITH  THE  ADJOINING  PART  OF  THE 
VENTRICULAR  WALL.  (From  a  drawing  by  V.  Horsley.) 

a,  endocardium,  prolonged  over  the  valve  ;  6,  sub-endocardial  tissue  ;  c,  fibrous  tissue  of  the 
valve,  thickened  at  c'  near  the  free  edge  ;  d,  section  of  the  lunula  ;  e,  section  of  the  fibrous 
ring  ;  /,  muscular  fibres  of  the  ventricle  attached  to  it ;  g,  loose  areolar  tissue  at  the  base 
of  the  ventricle  ;  s.  V.  sinus  Valsalvse  ;  1,  2,  3,  inner,  middle,  and  outer  coats  of  the  aorta. 

The  endocardium  (fig.  163,  B)  has  a  structure  not  very  unlike  the 
pericardium.     It  is  lined  by  a  pavement-epithelium  or  endothelium, 


142  THE  ESSENTIALS  OF  HISTOLOGY. 

like  that  of  a  serous  membrane,  and  consists  of  connective  tissue  with 
elastic  fibres  in  its  deeper  part,  between  which  there  may,  in  some 
parts,  be  found  a  few  plain  muscular  fibres.  Fat  is  sometimes  met 
with  under  the  endocardium. 

In  some  animals,  e.g.  the  sheep,  and  sometimes  also  in  man,  large 
beaded  fibres  are  found  under  the  endocardium.  These  are  formed  of 
large  clear  cells  joined  end  to  end,  and  generally  containing  in  their 
centre  two  nuclei,  whilst  the  peripheral  part  of  the  cell  is  formed 
of  cross-striated  muscular  tissue ;  they  are  known  as  the  fibres  of 
Purkinje. 

The  valves  of  the  heart  are  formed  of  folds  of  the  endocardium 
strengthened  by  fibrous  tissue  (fig.  165).  This  tissue  forms  a  thicken- 
ing near  the  free  edge  of  the  valve  (c').  At  the  base  of  the  auriculo- 
ventricular  valves  a  little  of  the  muscular  tissue  of  the  auricle  may  be 
found  passing  a  short  distance  into  the  valve. 

The  nerves  of  the  heart  are  seen  in  sections  underneath  the  epi- 
cardium  of  both  auricles  and  ventricles ;  in  the  former  situation  they 
are  connected  at  intervals  with  small  ganglia  (fig.  163,  g).  Their 
branches  pass  to  the  muscular  substance,  and  after  dividing  into  fine 
fibrils,  these  eventually  end  in  enlarged  extremities,  which  are  applied 
directly  to  the  muscular  fibres  (Ranvier). 


THE  TRACHEA  AND  LUNGS.  143 


LESSON    XXVII. 

THE  TRACHEA  AND  LUNGS. 

I.  IN  sections  of  the  trachea,  stained  with  hsematoxylin,  and  mounted  in 
Canada  balsam,  notice  the  ciliated  epithelium,  the  basement-membrane  (of 
some  thickness  in  the  human  trachea),  the  lymphoid  tissue  of  the  mucous 
membrane,  the  elastic  tissue  external  to  this,  and  lastly  the  fibrous  membrane 
containing  the  cartilages.  In  the  mucous  membrane  and  submucous  areolar 
tissue  look  for  sections  of  mucous  glands,  ducts  of  which  may  be  seen  opening 
on  the  surface.  At  the  back  of  the  trachea  notice  the  plain  muscular  fibres 
transversely  arranged  ;  there  may  be  larger  mucous  glands  external  to  these. 

2.  In  sections  of  lung  similarly  prepared,  notice  the  sections  of  the  alveoli 
collected  into  groups  (infundibula).     Find  sections  of  bronchial  tubes,  some 
cut  longitudinally  and  passing  at  their  extremities  into  the  infundibula, 
others  cut  across  ;  the  latter  show  the  structure  of  the  tubes  best.     In  each 
tube  notice  the  ciliated  epithelium  internally.     Next  to  this  the  mucous 
membrane  containing  numerous  elastic  fibres  and  often  thrown  into  folds  ; 
then  the  layer  of  circular  muscular  fibres,  and,  outside  this,  loose  fibrous  tissue 
in  which  in  larger  bronchial  tubes  the  pieces  of  cartilage  may  be  seen  em- 
bedded.    Small  mucous  glands  may  also  be  observed  in  the  fibrous  tissue 
sending  their  ducts  through  the  other  layers  to  open  on  the  inner  surface. 
Notice  always  accompanying  a  section  of  a  bronchial  tube  the  section  of  a 
branch  of  the  pulmonary  artery. 

In  the  sections  of  the  alveoli  observe  the  capillary  vessels  passing  from  one 
side  to  the  other  of  the  intervening  septa  ;  and  in  places  where  the  thin  wall 
of  an  alveolus  is  to  be  seen  in  the  section,  try  and  make  out  the  network  of 
blood-capillaries  upon  it.  Notice  within  the  alveoli  nucleated  corpuscles 
which  very  frequently  contain  dark  particles  in  their  protoplasm.  They  are 
amoeboid  cells  which  have  migrated  from  the  blood-vessels  and  lymphatics, 
and  have  taken  in  inhaled  particles  of  carbon.  They  seem  to  pass  back  into 
the  lung  tissue,  for  similar  cells  may  be  seen  in  this.  Make  a  sketch  of  part 
of  the  wall  of  a  bronchial  tube  and  of  one  or  two  of  the  alveoli. 

3.  In  sections  of  lung  the  air-cells  of  which  have  been  filled  with  a  mixture 
of  gelatine  and  nitrate  of  silver  solution  the  epithelium  of  the  alveoli  may  be 
studied.    The  sections  can  be  made  with  the  freezing  microtome,  and  mounted 
in  glycerine. 

4.  Mount  in  Canada  balsam  a  section  of  lung  in  which  the  pulmonary 
vessels  have  been  injected.     Study  the  general  arrangement  of  the  vessels 
with  a  low  power,  and  the  network  of  capillaries  of  the  alveoli  with  a  high 
power.     Observe  that   the  veins  run  apart  from  the  arteries.     Sketch  the 
capillary  network  of  one  or  two  adjoining  alveoli. 


The  trachea  or  windpipe  is  a  fibrous  and  muscular  tube,  the  wall  of 
which  is  rendered  somewhat  rigid   by  C-shaped   hoops   of  cartilage 


144 


THE  ESSENTIALS  OF  HISTOLOGY. 


which  are  embedded  in  the  fibrous  tissue.  The  muscular  tissue,  which 
is  of  the  plain  variety,  forms  a  flat  band,  the  fibres  of  which  run  trans- 
versely at  the  back  of  the  tube.  The  trachea  is  lined  by  a  muoc/us 
membrane  (fig.  166,  a-c),  which  has  a  ciliated  epithelium  upon  its 
inner  surface.  The  epithelium-cells  have  been  already  described 
(Lesson  VII.) ;  they  rest  upon  a  thick  basement  membrane.  The 
mucous  membrane  proper  consists  of  areolar  and  lymphoid  tissue,  and 
contains  numerous  blood-vessels  and  lymphatics.  In  its  deepest  part 
is  a  well-marked  layer  of  longitudinal  elastic  fibres  (d).  Many  small 
glands  for  the  secretion  of  mucus  are  found  in  the  wall  of  the  trachea. 
They  may  lie  either  within  the  mucous  membrane  or  in  the  submucous 


FIG.  166. — LONGITUDINAL  SECTION  OF  THE  HUMAN  TRACHEA,  INCLUDING  PORTIONS 
OF  TWO  CARTILAGINOUS  RINGS.     (Klein.)    (Moderately  magnified.) 

a,  ciliated  epithelium  ;  6,  basement-membrane :  c,  superficial  part  of  the  mucous  membrane, 
containing  the  sections  of  numerous  capillary  blood-vessels  and  much  lymphoid  tissue  ; 
d,  deeper  part  of  the  mucous  membrane,  consisting  mainly  of  elastic  fibres  ;  e,  submucous 
areolar  tissue,  containing  the  larger  blood-vessels,  small  mucous  glands  (their  ducts  and 
alveoli  are  seen  in  section),  fat,  etc. ;  /,  fibrous  tissue  investing  and  uniting  the  cartilages  ; 
g,  a  small  mass  of  adipose  tissue  in  the  fibrous  layer ;  ft,  cartilage. 

areolar  tissue  (e),  or,  lastly,  at  the  back  of  the  trachea,  outside  the 
transverse  muscular  fibres. 

The  two  divisions  of  the  trachea,  the  bronchi,  are  precisely  similar  in 
structure. 

The  larynx  is  also  very  like  the  trachea  so  far  as  the  structure  of 


THE  TRACHEA  AND  LUNGS. 


145 


the  mucous  membrane  is  concerned,  but  over  the  true  vocal  cords  and 
upon  the  epiglottis,  as  well  as  here  and  there  in  the  part  above  the 
glottis,  stratified  epithelium  is  found,  and  taste-buds  (see  next  Lesson) 
may  occur  in  this  epithelium,  except  over  the  vocal  cords. 


FIG  167.— DIAGRAMMATIC  REPRESENTATION  OF  THE  ENDING  OF  A 
BRONCHIAL  TUBE  IN  SACCULATED  INFUNDIBULA. 

J3,  terminal  bronchus  ;  L.B.,  lobular  bronchiole  ;  A,  atrium  ;  I,  infundibulum  ;  C,  air-cells 

or  alveoli. 

The  lymphoid  tissue  is  especially  abundant  in  the  mucons  mem- 
brane of  the  ventricle  of  Morgagni,  and  a  large  number  of  mucous 
glands  open  into  this  cavity  and  into  that  of  the  sacculus. 

The  true  vocal  cords  are  composed  of  fine  elastic  fibres. 


FIG.  168. — PORTION  OF  A  TRANSVERSE  SECTION  OF  A  BRONCHIAL  TUBE,  HUMAN, 
6  MM.  IN  DIAMETER.     (F.  E.  Schultze.)     (Magnified  30  diameters.) 

a,  cartilage  and  fibrous  layer  with  mucous  glands,  and,  in  the  outer  part,  a  little  fat  ;  in  the 
middle,  the  duct  of  a  gland  opens  on  the  inner  surface  of  the  tube  ;  b,  annular  layer  of 
involuntary  muscular  fibres ;  c,  elastic  layer,  the  elastic  fibres  in  bundles  which  are  seen 
cut  across  ;  d ,  columnar  ciliated  epithelium. 

K 


146 


THE  ESSENTIALS  OF  HISTOLOGY. 


The  cartilages  of  the  trachea  and  larynx  are  hyaline,  except  the 
epiglottis  and  the  cartilages  of  Santorini  and  of  Wrisberg,  which  are 
composed  of  elastic  fibro-cartilage. 

The  lungs  are  formed  by  the  ramifications  of  the  bronchial  tubex 
and  their  terminal  expansions,  which  form  groups  of  sacculated  dila- 
tations (infundibula),  beset  everywhere  with  small  hemispherical 
bulgings,  known  as  the  air-cells  or  pulmonary  alveoli. 

The  bronchial  tubes  (figs.  168,  169)  are  lined  in  their  whole  extent 
by  ciliated  epithelium  which  rests  on  a  basement  membrane.  External 
to  this  is  the  corium  of  the  mucous  membrane,  containing  a  large 
number  of  longitudinal  elastic  fibres  and  some  lymphoid  tissue.  Out- 
side this  again  is  a  complete  layer  of  plain  muscular  fibres  encircling 
the  tube.  Next  comes  a  loose  fibrous  layer  in  which,  in  the  larger 
tubes  (fig.  168),  small  plates  of  cartilage  are  embedded.  Mucous 
glands  are  also  present  in  this  tissue. 


cL      c      O 


FIG.  169.— SECTION  OF  A  SMALL  BKONCHIAL  TUBE  FROM  THE  PIG'S  LUNG. 
(F.  E.  Schultze.)  (This  section  is  much  more  magnified  than  that  represented 
in  the  previous  figure.) 

a,  fibrous  layer  ;  6,  muscular  layer  ;  c,  mucous  membrane  in  longitudinal  folds,  with  numer- 
ous longitudinally  running  elastic  fibres  cut  across  ;  d,  ciliated  epithelium  ;  /,  surround- 
ing alveoli. 

The  smallest  bronchial  tubes,  which  are  about  to  expand  into  the 
infundibula,  gradually  lose  the  distinctness  of  the  several  layers,  their 
wall  at  the  same  time  being  greatly  thinned  out  and  becoming  bulged 
to  form  the  alveoli.  The  epithelium  also  becomes  changed  ;  from 
columnar  and  ciliated  it  becomes  cubical  and  non-ciliated. 

In  the  alveoli  themselves,  besides  small  groups  of  cubical  cells 
there  are  large  irregular  flattened  cells  (fig.  170),  which  form  an 
extremely  delicate  layer,  separating  the  blood-capillaries  from  the  air 


THE  TRACHEA  AND  LUNGS. 


147 


FIG.  170.— SECTION  OF  PART  OF  CAT'S  LUNG,  STAINED  WITH  NITRATE  OF  SILVER. 
(Klein. )    ( Highly  magnified. ) 

The  smalf  granular  and  the  large  flattened  cells  of  the  alveoli  are  shown.  In  the  middle 
is  a  section  of  a  lobular  bronchial  tube,  with  a  patch  of  the  granular  pavement- 
epithelium  cells  on  one  side. 


.  171. — SECTION  OF  INJECTED  LUNG,  INCLUDING  SEVERAL  CONTIGUOUS  ALVEOLI. 

(F.  E.  Schultze.)     (Highly  magnified.) 

a,  free  edges  of  alveoli ;  c,  c,  partitions  between  neighbouring  alveoli,  seen  in  section ; 
6,  small  arterial  branch  giving  off  capillaries  to  the  alveoli.  The  looping  of  the  vessels 
to  either  side  of  the  partitions  is  well  exhibited.  Between  the  capillaries  is  seen  the 
homogeneous  alveolar  wall  with  nuclei  of  connective  tissue  corpuscles  and  elastic  fibres. 


148  THE  ESSENTIALS  OF  HISTOLOGY. 

within  the  alveoli.  The  capillary  network  of  the  alveoli  is  very 
close  (fig.  171),  and  the  capillary  vessels  of  adjoining  alveoli  are  in 
complete  continuity,  the  vessels  passing  first  to  one  side  and  then  to 
the  other  of  the  septa  which  separate  the  adjacent  alveoli. 

Blood-vessels. — Branches  of  the  pulmonary  artery  accompany  the 
bronchial  tubes  to  be  distributed  to  the  capillary  networks  upon  the 
alveoli,  from  which  the  blood  is  returned  by  the  pulmonary  veins. 
These,  pursuing  a  separate  course  through  the  tissue  of  the  lung,  join 
in  their  course  with  others  to  form  larger  vessels  which  pass  to  the 
Jiilum.  Branches  from  the  bronchial  arteries  are  distributed  to  the 
walls  of  the  bronchial  tubes,  and  to  the  connective  tissue  of  the  lung. 
This  tissue  intervenes  everywhere  in  small  quantity  between  the 
infundibula  (interstitial  tissue),  and  forms  a  distinct  layer,  containing 
much  elastic  tissue,  covering  the  surface  of  the  lung  underneath  the 
serous  membrane  (subserous  tissue.)  In  some  animals  (e.g.  guinea-pig) 
this  subserous  layer  contains  plain  muscular  tissue,  which  is  especially 
developed  near  the  lung-apex,  but  it  has  not  been  detected  in  man. 

The  lymphatics  of  the  lung  form  two  sets  of  vessels,  one  set  accom- 
panying the  bronchial  tubes,  and  another  set  forming  a  network  in  the 
interstitial  connective  tissue,  and  in  the  subserous  tissue.  Both  sets  of 
lymphatics  tend  towards  the  hilum,  and  enter  lymphatic  glands  at  the 
root  of  the  lung.  Those  in  the  subserous  tissue  communicate  by  means 
of  stomata  between  the  epithelial  cells  of  the  serous  membrane  with  the 
cavity  of  the  pleura. 

The  pleura,  which  covers  the  surface  of  the  lung,  has  the  usual  struc- 
ture of  a  serous  membrane.  It  is  provided  with  a  special  network  of 
capillary  blood-vessels,  which  are  supplied  by  branches  of  the  bronchial 
arteries. 


STRUCTURE  OF  THE  TEETH.  149 


LESSON  XXVIII. 

STRUCTURE  OF  THE  TEETH,  THE  TONGUE,  AND  MUCOUS 
MEMBRANE  OF  THE  MOUTH. 

1.  STUDY  first  with  the  low  power  and  afterwards  with  the  high  power  a 
longitudinal  section  of  a  human  tooth  which  has  been  prepared  by  grinding. 
It  is  better  to  purchase  this  specimen,  for  the  process  of  preparation  is 
difficult  and  tedious  without  the  aid  of  special  apparatus.  Examine  carefully 
the  enamel,  the  dentine,  and  the  cement.  The  dark  appearance  of  the 
deiitinal  tubules  is  due  to  their  containing  air  in  the  dried  specimen. 
Measure  the  diameter  of  the  enamel  prisms  and  of  some  of  the  dentinal 
tubules.  Make  sketches  from  each  of  the  tissues. 

2.  Mount  in  Canada  balsam  a  section  of  a  tooth,  in  situ,  which  has  been 
decalcified    in   chromic   or   nitric   acid   and    stained   with    hsematoxylin    or 
carmine.     In  this  section  the  mode  of  implantation  of  a  tooth,  as  well,  as  the 
structure  of  the  pulp,  can  be  made  out.     Make  a  general  sketch  under  a  low 
power,  and  under  a  high  power  draw  a  small  piece  of  the  pulp  showing  the 
processes  of  the  odontoblasts  extending  into  the  dentinal  tubules. 

3.  The  development  of  the  teeth  and  the  formation  of  their  tissues  are 
studied  in  sections  made  across  the  snout  and  lower  jaw  of  foetal  animals. 
The  preparation  should  be  stained  in  bulk  with  alcoholic  magenta,  borax- 
carmine,  or  hsematoxylin,  and  embedded  in  paraffin  or   celloidin  •    if    the 
former,  the  sections  must  be  mounted  by  an  adhesive  process  (see  Appendix). 

4.  Sections  of  the  tongue  vertical  to  the  surface  ;  stain  with  hsematoxyliii, 
and  mount  in  Canada  balsam.     In  these  sections  the  arrangement  of  the 
muscular  fibres  and  the  structure  of  the  papillae  of  the  mucous  membrane 
may  be  studied  ;  and  if  the  organ  have  been  previously  injected,  the  arrange- 
ment of  the  blood-vessels  in  the  muscular  tissue  and  in  the  mucous  membrane 
will  also  be  well  seen. 


THE  TEETH. 

A  tooth  consists  in  man  of  three  calcified  tissues  :  the  enamel,  which 
is  of  epithelial  origin,  the  dentine,  and  the  cement,  or  crusta  petrosa.  The 
dentine  forms  the  main  substance  of  a  tooth,  the  enamel  covers  the 
erown,  and  the  cement  is  a  layer  of  bone  which  invests  the  root  (fig.  172). 

The  enamel  is  formed  of  elongated  hexagonal  prisms  (fig.  173),  which 
are  set  vertically,  or  with  a  slight  curvature,  upon  the  surface  of  the 
dentine.  They  are  marked  at  tolerably  regular  intervals  with  slight 
transverse  shadings  producing  an  indistinct  cross-striated  appearance. 
Sometimes  coloured  lines  run  through  the  enamel  across  the  direction 
of  its  fibres. 


150 


THE  ESSENTIALS  OF  HISTOLOGY. 


The  dentine  is  composed  of  a  hard  dense  substance  like  bone,  bnt 
containing  no  Haversian  canals  or  lacunae.  It  is  pierced  everywhere, 
however,  by  fine  canaliculi  (dentinal  tubules,  figs.  175,  176),  radiat- 
ing outwards  from  a  central  cavity  which,  during  life,  contains  the 
pulp.  The  tubules  branch  at  acute  angles  as  they  pass  outwards  ; 
their  branches  become  gradually  finer  towards  the  periphery  of  the 


FIG.  172.  —  VERTICAL 
SECTION  OF  A  TOOTH 
in  situ.  (15  diame- 
ters.) (Waldeyer.) 

c,  is  placed  in  the  pulp- 
cavity,  opposite  the 
cervix  or  neck  of  the 
tooth ;  the  part  above 
is  the  crown,  that  below 
is  the  root  (fang).  lr 
enamel  with  radial  and 
concentric  markings ; 

2,  dentine  with  tubules 
and  incremental  lines  ; 

3,  cement  or  crusta  pe- 
trosa,  with  bone-corpus- 
cles ;   4,   dental  perios- 
teum ;  5,  bone  of  lowei~ 
jaw. 


dentine.  The  tubules  have  a  proper  wall  of  their  own,  which  can  be 
isolated  by  steeping  a  section  of  tooth  in  strong  hydrochloric  acid.  In 
the  living  tooth  they  are  occupied  by  protoplasmic  fibres,  which  are  pro- 
longed from  the  superficial  cells  of  the  pulp. 

The  intertubular  substance  appears  for  the  most  part  homogeneous,, 
but  here  and  there  indications  can  be  seen  in  it  of  a  globular  forma- 


STRUCTURE  OF  THE  TEETH. 


151 


tion.     This  is  especially  the  case  near   the  surface   of   the   dentine, 
where  the  globular  deposit  and  the  interglobular  spaces  may  produce 


FIGS.  173  AND  174.— ENAMEL  PRISMS.     (350  diameters.)    (Kolliker.) 

Fig.  173.— Fragments  and  single  fibres  of  the  enamel,  isolated  by  the  action  of  hydrochloric  acid. 
Fig.  174.— Surface  of  a  small  fragment  of  enamel,  showing  the  hexagonal  ends  of  the  fibres. 


FIG.  175. — SECTION  OF  FANG,  PARALLEL 

TO  THE  DENTINAL  TUBULES.       (Magni- 
fied 300  diameters.)     (Waldeyer.) 
1,  cement,  with  large  bone  lacunae  and  indi- 
cations of  lamellae  ;   2,  granular  layer  of 
Purkiiije  (interglobular  spaces) ;  3,  dentinal 
tubules. 


-°-"= 


FIG.  176.— SECTIONS  OF  DENTJNAL 

TUBULES.    (Fraenckel.) 

a,  cut  across  ;  6,  cut  obliquely. 

(About  300  diameters.) 


152 


THE  ESSENTIALS  OF  HISTOLOGY. 


a  granular  appearance  (granular  layer,  fig.  175,  2),  and  also  in  the 
course  of  certain  lines  or  clefts  which  are  seen  traversing  the  dentine 
across  the  direction  of  the  tubules  (incremental  lines,  fig.  172,  shown 
magnified  in  fig.  177).  The  dentine  can  be  separated  into  lamellae 
along  these  incremental  lines. 

The  animal  matter  of  dentine  resembles  bone  and  the  connective 
tissues  generally  in  having  its  ground  substance  pervaded  by  fibres 
which  yield  gelatine  on  boiling.  These  fibres,  which  have  been 
especially  investigated  by  v.  Ebner  and  by  Mummery,  are  difficult  of 
demonstration  in  the  fully  calcified  dentine  ;  but  in  developing 
dentine  and  in  dentine  which  is  attacked  by  caries  they  are  more 
easily  shown. 


FlG.    177. — A  SMALL  PORTION  OF  DENTINE  WITH  1NTERGLOBULAR  SPACES. 

(Kolliker.)     (350  diameters.) 

c,  portion  of  incremental  line  formed  by  the  interglobular  spaces,  which  are  here  filled  up 
by  a  transparent  material. 

The  pulp  consists  of  a  soft,  somewhat  jelly-like,  connective  tissue, 
containing  many  branched  cells,  a  network  of  blood-vessels,  and  some 
nerve-fibres  which  pass  into  the  pulp-cavity  along  with  the  blood- 
vessels by  a  minute  canal  at  the  apex  of  the  fang.  The  superficial 
cells  of  the  pulp  form  an  almost  continuous  layer,  like  an  epithelium. 
They  are  known  as  odontoblasis,  from  having  been  concerned  in  the 
formation  of  the  dentine. 

The  crusta  petrosa  ;(fig.  175,  1)  is  a  layer  of  lamellated  bone  in- 
cluding lacunae  and  canaliculi,  but  without  Haversian  canals,  at  least 
normally  in  the  human  teeth.  It  is  covered  with  periosteum  (dental 
periosteum),  which  also  lines  the  socket,  and  serves  to  fix  the  tooth 
securely. 

Formation  of  the  teeth. — The  teeth  are  developed  in  the  same 
manner  as  the  hairs.  A  thickening  of  the  epithelium  occurs  along  the 
line  of  the  gums,  and  grows  into  the  corium  of  the  mucous  membrane 


DEVELOPMENT  OF  THE  TEETH.  153 

(common  enamel-germ,  fig.  178,  A).  At  regular  intervals  there  is  yet  a 
further  thickening  and  growth  from  the  common  enamel-germ  into  the 
tissue  of  the  mucous  membrane,  each  of  these  special  rudiments  swelling 
out  below  into  a  flask-shaped  mass  of  cells,  the  special  enamel-germ, 
fig.  178,  B).  A  vascular  papilla  grows  up  from  the  corium  into  the 
bottom  of  the  special  enamel-germ  (fig.  178,  C,  D) ;  this  papilla  has 
the  shape  of  the  crown  of  the  future  tooth.  Each  special  enamel- 
germ,  with  its  included  papilla,  presently  becomes  cut  off  from  the 
epithelium  of  the  mouth,  and  surrounded  by  a  vascular  membrane — 
the  dental  sac.  The  papilla  becomes  transformed  into  the  dentine  of 
the  future  tooth,  and  the  enamel  is  deposited  upon  its  surface  by  the 
epithelial-cells  of  the  enamel-germ.  The  root  of  the  tooth,  with  its 
covering  of  cement,  is  formed  at  a  later  period,  when  the  tooth  is 
beginning  to  grow  up  through  the  gum,  by  a  gradual  elongation  of  the 
base  of  the  papilla. 

Previously  to  the  deposition  of  the  enamel,  the  enamel-germ  under- 
goes a  peculiar  transformation  of  its  previously-rounded  epithelium- 
cells  into  three  layers  of  modified  cells.  One  of  these  is  a  layer  of 
columnar  cells  (fig.  179,  d\  which  immediately  covers  the  surface 
of  the  dentine.  These  columnar  cells  form  the  enamel-prisms  either 
by  a  deposition  of  calcareous  salts  external  to  them,  or  by  a  direct 
calcification  of  their  protoplasm.  The  cells  next  to  the  dental  sac 
form  a  single  layer  of  cubical  epithelium  (e),  nearly  all  the  other  cells 
of  the  enamel-germ  become  transformed  into  branching  corpuscles  (c) 
communicating  by  their  processes,  and  thus  forming  a  continuous  net- 
work. The  enamel-germ,  after  it  is  thus  modified,  is  known  as  the 
enamel-organ. 

The  dentine  of  the  tooth  is  formed  by  calcification  of  the  surface  of 
the  papilla.  At  this  surface  there  is  a  well-marked  layer  of  odonto- 
blasts  (fig.  180),  and  these  produce  a  layer  of  dentinal  matrix  which 
forms  a  sort  of  cap  to  the  papilla,  and  which  soon  becomes  calcified  by 
the  deposition  of  globules  of  calcareous  matter.  Processes  of  the  odonto- 
blasts  remain  in  the  dentine  as  it  is  forming,  and  thus  the  dentinal 
tubules  are  produced.  Subsequently  other  layers  of  dentine  are  formed 
within  the  first  by  a  repetition  of  the  same  process,  and  in  this  way  the 
papilla  gradually  becomes  calcified.  A  part,  however,  remains  un- 
altered in  the  centre  of  the  tooth,  and  with  its  covering  of  odontoblasts 
forms  the  pulp. 

The  ten  milk-teeth  are  formed  in  each  jaw  in  this  manner.  These, 
however,  become  lost  within  a  few  years  after  birth,  and  are  replaced 
by  permanent  teeth  in  much  the  same  way  that  a  new  succession  of 
hairs  occurs.  A  small  outgrowth  takes  place  at  an  early  period  from 


154 


THE  ESSENTIALS  OF  HISTOLOGY. 

A  B 


FIG.  178. 

A.  SECTION  ACROSS  THE  UPPER  JAW  OF  A  FCETAL  SHEEP.     (3  centimeters  long.) 

(Waldeyer.) 

1,  common  enamel-germ  dipping  down  into  the  mucous  membrane  where  it  is  half  surrounded 
by  a  horseshoe-shaped  more  dense-looking  tissue,  the  germ  of  the  dentine  and  dental  sac; 
2,  palatine  process  of  the  maxilla. 

B.  SECTION   SIMILAR   TO    THAT    SHOWN   IN    THE    PREVIOUS    FIGURE,    BUT    I>ASSI_\<; 

THROUGH     ONE     OF     THE    SPECIAL     ENAMEL-GERMS     HERE     BECOMING     FLASK-SHAPED. 

(Kolliker.) 

c,  c',  epithelium  of  mouth  ;  /,  neck  ;  f,  body  of  special  enamel-germ. 

C  AND  D.  SECTIONS  AT  LATER  STAGES  THAN  A  AND  B,  THE  PAPILLA  HAVING  BE- 
COME FORMED  AND  HAVING  INDENTED  THE  ENAMEL-GERM,  WHICH  HAS  AT  THE  SAME 
TIME  GROWN  PARTLY  ROUND  IT.  (Kolliker.) 

,  epithelium  of  gum,  sketched  in  outline  ;  /,  neck  of  enamel-germ  ;  /',  enamel-organ  ;  e,  its 
deeper  columnar  cells  ;  e',  projections  into  the  corium  ;  p,  papilla  ;  s,  dental  sac  forming. 
In  D,  the  enamel-germ  (fp)  of  the  corresponding  permanent  tooth  has  become  formed. 


DEVELOPMENT  OF  THE  TEETH. 


155 


the  enamel-germ  of  each  of  the  milk-teeth  (fig.  178,  D,/»,  and  this 
eventually  becomes  the  germ  of  the  corresponding  permanent  tooth. 
It  gradually  enlarges,  acquires  a  papilla,  forms  an  enamel-organ,  in 


FIG.    179.  —  A     SECTION     THROUGH    THE 

ENAMEL-ORGAN    AND    DENTAL    SAC     FROM 
THE   TOOTH  OF  A  CHILD    AT    BIRTH.      (250 

diameters.)     (Kolliker.) 

a,  outer  dense  layer  of  the  dental  sac  ;  b,  inner 
looser  texture  of  the  same  with  capillary  blood- 
vessels and  a  somewhat  denser  layer  towards 
the  enamel-organ ;  c,  spongy  substance ;  d, 
inner  cells  ;  and  e,  outer  cellular  layer  of  the 
enamel-organ. 


FIG.  180. — PART  OF  SECTION  OF  DEVELOP- 
ING TOOTH  OF  YOUNG  RAT,  SHOWING 
THE  MODE  OF  DEPOSITION  OF  THE  DEN- 
TINE. (Highly  magnified.) 

«,  outer  layer  of  fully  calcified  dentine ;  I,  un- 
calcified  matrix,  with  a  few  nodules  of  calca- 
reous matter ;  c,  odontoblasts  with  processes 
extending  into  the  dentine ;  d,  pulp.  The 
section  is  stained  with  carmine,  which  colours 
the  uncalcified  matrix,  but  not  the  calcined 
part. 


iort,  passes  through  the  same  phases  of  development  as  its  parent 
germ,  and  when  the  milk-tooth  drops  out  of  the  jaw  in  consequence  of 
the  absorption  of  its  roots  (by  osteoclasts)  the  permanent  tooth  grows 
up  into  its  place. 

But  there  are  six  permanent  teeth  in  each  jaw  which  do  not  succeed 


156  THE  ESSENTIALS  OF  HISTOLOGY. 

milk-teeth  ;  these  are  the  permanent  molars.  They  are  developed  from 
an  extension  backwards  of  the  original  epithelial  thickening  or  common 
enamel-germ  and  the  downgrowth  from  this  into  the  corium  of  three 
successive  special  enamel -germs  at  comparatively  long  intervals  of  time. 
Within  these  the  tissues  of  the  permanent  molars  become  formed  in  a 
manner  exactly  similar  to  that  in  which  the  milk-teeth  are  developed. 


THE  TONGUE. 

The  tongue  is  mainly  composed  of  striated  muscular  fibres,  running, 
some  longitudinally,  and  others  transversely.  It  is  covered  by  a  mucous 
membrane,  the  epithelium  of  which,  like  that  of  the  rest  of  the  mouth, 
is  thick  and  stratified,  and  conceals  microscopic  papillae  (fig.  181)  like 
those  of  the  skin.  Besides  these,  the  upper  surface  of  the  organ  is 
covered  with  larger  papillae,  which  give  it  a  rough  appearance.  These, 
which  are  termed  the  lingual  papillce,  are  of  three  kinds  :  (1)  About  twelve 
or  thirteen  comparatively  large  circular  projections,  each  of  which  is 
surrounded  by  a  narrow  groove  (fossa),  external  to  which  the  mucous 
membrane  is  raised  above  the  general  level  (vallum)  (fig.  182).  These 
papillae  form  a  V-shaped  line  towards  the  back  of  the  tongue ;  they 
receive  filaments  of  the  glosso-pharyngeal  nerve,  and  have  taste-buds  in 
the  epithelium  which  covers  their  sides,  and  in  that  of  the  side  of  the 
vallum.  They  are  known  as  the  circumvallate  papillce.  (2)  All  the  rest 
of  the  papillary  surface  of  the  tongue  is  covered  by  conical  papillce,  so 
named  from  the  conical  pointed  cap  of  epithelium  which  is  borne  by 
each  ;  sometimes  this  cap  is  fringed  with  fine  epithelial  filaments,  when 
they  are  termed  filiform  (fig.  184).  (3)  Scattered  here  and  there 
amongst  the  conical  papillae  are  other  larger  papillae,  the  fungiform 
(fig.  183).  These  are  very  vascular,  and  lie  partly  embedded  in  little 
depressions  of  the  mucous  membrane. 

Small  tubular  glands  may  be  seen  between  the  superficial  muscular 
fibres  sending  their  ducts  to  the  surface.  Most  of  them  secrete  mucus, 
but  those  which  open  into  the  trenches  of  the  circumvallate  papillae, 
and  a  few  others  elsewhere,  yield  a  serous  secretion  (glands  of  Ebner). 

The  mucous  membrane  at  the  back  of  the  tongue  contains  a  large 
amount  of  lymphoid  tissue. 

The  taste-buds. — The  minute  gustatory  organs  which  are  known  as 
taste-buds  may  be  seen  in  sections  which  pass  through  the  papillae 
vallatae  or  the  papillae  fungiformes;  they  are  also  present  here  and 
there  in  the  epithelium  of  the  general  mucous  membrane  of  the  tongue, 
especially  at  the  back  and  sides,  and  occur  also  upon  the  under  surface 


THE  TONGUE. 


FIG.  181. — SECTION  OF 

MUCOUS  MEMBRANE 
OF  MOUTH,  SHOWING 
THEEE  MICROSCOPIC 
PAPILLAE  AND  STRA- 
TIFIED EPITHELIUM. 
THE  BLOOD-VESSELS 
HAVE  BEEN  INJECTED. 

(Tolclt.) 


FIG.   182. — SECTION    OF  CIRCUMVALLATE  PAPILLA, 

HUMAN.      THE  FIGURE  INCLUDES  ONE  SIDE  OF  THE 
PAPILLA     AND     THE     ADJOINING     PART     OF     THE 

VALLUM.  (Magnified  150 diameters.)  (Heitzmann.) 
E.  epithelium  ;  G,  taste-bud ;  C,  corium  with  injected 
blood-vessels  ;  M,  gland  with  duct. 


FIG.  183. — SECTION  OF  FUNGIFORM 
PAPILLA,  HUMAN.  (Heitzmann.) 

E,  epithelium  ;  C,  corium  ;  Z,  lymphoid 
tissue  ;  M,  muscular  fibres  of  tongue. 


FIG.    184. — SECTION    OF    TWO 

FILIFORM     PAPILLA,     HUMAN. 

(Heitzmann.)     (Letters  as  in 
previous  figure. ) 


158 


THE  ESSENTIALS  OF  HISTOLOGY. 


of  the  soft  palate,  and  on  the  epiglottis.  But  they  are  most  easily 
studied  in  the  papillae  foliatae  of  the  rabbit,  two  small  oval  areas  lying 
on  either  side  of  the  back  of  the  tongue  and  marked  transversely  with 
a  number  of  small  ridges  or  laminee  with  intervening  furrows  (see 


FIG.  185.— TONGUE  OF  BABBIT,  SHOWING  THE  SITUATION  OF  THE 

PAPILLA  FOLIATE,  p. 

figs.  185  and  186).     Sections  across  the  ridges  show  numerous  taste- 
buds  embedded  in  the  thick  epithelium  which  clothes  their  sides. 

The  taste-buds  are  ovoid  clusters  of   epithelium-cells  which  lie  in 
cavities  in  the  stratified  epithelium  (fig.  187).     The  base  of  the  taste- 


FIG.  186.— VERTICAL  SECTION  OF  PAPILLA  FOLIATA  OF  THE  RABBIT,  PASSING 
ACROSS  THE  FOLi.E.      (Ranvier. ) 

•p,  central  lamina  of  the  corium  ;  v,  section  across  a  vein,  which  traverses  the  whole  length 
of  the  folia :  p',  lateral  lamina  in  which  the  nerve-fibres  run  ;  g,  taste-bud  ;  n,  sections  of 
nerve-bundles  :  a,  serous  gland. 

Tjud  rests  upon  the  corium  of  the  mucous  membrane,  and  receives  a 
branch  of  the  glosso-pharyngeal  nerve ;  the  apex  is  narrow  and  com- 
municates with  the  cavity  of  the  mouth  by  a  small  pore  in  thev  super- 
ficial epithelium  (gustatory  pore,  fig.  187,  j?). 


THE  GUSTATORY  ORGANS. 


159 


The  cells  which  compose  the  taste-bud  are  of  two  kinds,  viz.  : 
1.  The  gustatory  cells  (fig.  188,  a),  which  are  delicate  fusiform  or 
bipolar  cells  composed  of  the  cell-body  or  nucleated  enlargement,  and 
of  two  processes,  one  distal,  the  other  proximal.  The  distal  process  is 


FIG.  187.— SECTION  THROUGH  THE  MIDDLE  OF  A  TASTE-BUD.     (Eanvier.) 

p,  gustatory  pore  ;  s,  gustatory  cell ;  r,  sustentacular  cell ;  m,  lymph  cell,  containing  fatty 
granules  ;  e,  sup3rficial  cells  of  the  stratified  epithelium  :  n,  nerve-fibres. 

nearly  straight,  and  passes  towards  the  apex  of  the  taste-bud,  where  it 
terminates  in  a  small,  highly  refracting  cilium-like  appendage,  which 
projects  into  the  pore  above  mentioned.  The  proximal  process  is  more 


FIG.  188. — VARIOUS  CELLS  FROM  TASTE-BUD  OF  RABBIT.     (Engelmann.) 
(600  diameters.) 


«  four  gustatory  cells  from  central  part ;  6,  two  sustentacular  cells,  and  one  gustatory  cell,  in 
connection ;  c,  three  sustentacular  cells. 


icate  than  the  other,  and  is   often   branched    and  varicose ;    it  is 
ieved  to  be  directly  connected   with  a  nerve-fibre.     In  such  case, 


160  THE  ESSENTIALS  OF  HISTOLOGY. 

the  nerve-fibre  may  be  supposed  to  take  origin  in  the  gustatory 
cell.  A  similar  arrangement  obtains  in  the  olfactory  organ.  2.  The 
xustentamlar  cells  (fig.  188,  c).  These  are  elongated  cells,  mostly  flat- 
tened, and  pointed  at  their  ends ;  they  lie  between  the  gustatory  cells, 
which  they  thus  appear  to  support,  and  in  addition  they  form  a  sort  of 
envelope  or  covering  to  the  taste-bud.  Between  the  cells  of  the  taste- 
bud  lymph-corpuscles  are  often  seen,  having  probably  wandered  hither 
from  the  subjacent  mucous  membrane. 


THE  SALIVARY  GLANDS.  161 


LESSON  XXIX. 


THE   SALIVARY  GLANDS. 

1.  STUDY  carefully  sections  of  the  submaxillary  gland  of  a  dog.  The  gland 
may  be  hardened  in  alcohol  and  stained  with  luematoxylin.  Notice  the  acini 
filled  with  clear  cells,  the  nuclei  of  which  usually  lie  near  the  basement-mem- 
brane. Notice  here  and  there,  outside  the  clear  cells,  demilunes  or  crescents 
of  small  darkly  stained  granular-looking  cells.  Observe  also  the  sections  of 
the  ducts  with  their  striated  columnar  epithelium.  Try  and  find  a  place 
where  one  of  the  ducts  is  passing  into  the  alveoli.  Sketch  under  a  high 
power. 

2.  Study  sections  of  the  parotid  gland  prepared  in  a  similar  way. 

3.  Examine  small  pieces  of  both  submaxillary  and  parotid  gland  of  the  dog 
fresh  in  2  per  cent,  salt  solution.      In  the  submaxillary  gland  notice  that  the 
alveolar-cells  are  swollen  out  with  large  granules  or  droplets  of  mucigen, 
which  swell  up  in  water  to  form  large  clear  vacuoles.     Dilute  acids  and 
alkalies  produce  a  similar  change.     The  cells  of  the  parotid  gland  are  also 
filled  with  granules  (zymogen),  but  they  are  smaller,  and  simply  dissolve  in 
watery  fluids.1     Make  a  sketch  from  each  preparation  under  a  high  power. 

4.  Prepare   a   transverse   section   of   the   oesophagus.      Notice   the   thick 
muscular  coat  partly  containing  cross-striated  fibres  and  the  mucous  mem- 
brane with  its  papilla?  and  stratified  epithelium.     Look  for  mucous  glands  in 
the  areolar  coat.     Sketch  under  a  low  power. 


The  salivary  glands  may  be  looked  upon  as  typical  of  secreting 
glands  in  general.  They  are  composed  of  a  number  of  lobules  bound 
together  loosely  by  connective  tissue.  Each  small  lobule  is  formed  of 
a  group  of  saccular  or  somewhat  tubular  alveoli  or  acini  (fig.  189)  from 
which  a  duct  passes,  and  this,  after  uniting  with  other  ducts  to  form 
larger  and  larger  tubes,  eventually  leaves  the  gland  to  open  upon  the 
surface  of  the  mucous  membrane  of  the  mouth. 

The  alveoli  are  inclosed  by  a  basement-membrane,  which  is 
reticular  (fig.  190).  This  basement-membrane  is  continued  along  the 
ducts.  Within  it  is  the  epithelium,  which  in  the  alveoli  is  composed  of 
polyhedral  cells  (fig.  191,  a),  but  in  the  ducts  is  regularly  columnar, 

1  To  study  the  changes  which  the  alveolar  cells  undergo  during  secretion,  pilocarpine  is 
injected  subcutaneously  into  an  animal  in  sufficient  amount  to  produce  copious  saliva- 
tion ;  after  which  the  animal  is  killed  and  its  salivary  glands  are  examined  as  in  prepara- 
tion 3.  The  granules  are  not  seen  in  preparations  that  have  been  in  alcohol,  but  osmic 
acid  preserves  them  ;  they  are  best  seen  in  the  fresh  tissue. 

L 


THE  ESSENTIALS  OF  HISTOLOGY. 


FIG.  189.—  DIAGRAM  OF  THE  CONSTRUCTION  OK  A  LOBULE  OF  A  TUBULO-RACEMOSK 
(ACINO-TUBULAR)  MUCOUS  GLAND.     (Kolliker.) 

«,  duct ;  b,  a  branch  of  the  duct ;  c,  alveoli  as  they  lie  together  in  the  gland  ;  d,  the  same 
separated,  showing  their  connection  as  an  irregular  tube. 


FIG.  190.— MEMBRANA  PROPRIA  OF  TWO  ALVEOLI  ISOLATED.     (Heidenhain. ) 

The  preparation  is  taken  from  the  orbital  gland  of  the  dog,  which  is  similar  in  structure  to 
a  mucous  salivary  gland. 


FIG.  191.— SECTION  OF  THE  SUBMAXILLARY  GLAND  OF  THE  DOG,  SHOWING  THE 
COMMENCEMENT  OF  A  DUCT  IN  THE  ALVEOLI.     (Magnified  425  diameters.) 

a,  one  of  the  alveoli,  several  of  which  are  in  the  section  shown  grouped  around  the 
commencement  of  the  duct  d'  ;  a',  an  alveolus,  not  opened  by  the  section  ;  b,  basement- 
membrane  in  section  ;  c,  interstitial  connective  tissue  of  the  gland ;  d,  section  of  a  duct 
which  has  passed  away  from  the  alveoli,  and  is  now  lined  with  characteristically  striated 
columnar  cells  ;  s,  semilunar  group  of  darkly  stained  cells  at  the  periphery  of  an  alveolus. 


THE  SALIVARY  GLANDS.  163 

except  in  that  part  of  the  duct  which  immediately  opens  into  the 
alveoli  (functional  part)  •  in  this  it  is  flattened  (d').  The  columnar 
epithelium  of  the  ducts  is  peculiar,  in  that  the  cells  show  a  distinction 
into  two  unequal  zones,  an  outer,  larger,  striated  zone,  and  an  inner, 
smaller,  granular  one  (fig.  191,  d). 


FIG.  192.— SECTION  OF  DOG'S  SUBMAXILLABY,  STAINED.    (Kolliker. 
a,  duct ;  b,  alveolus  ;  c.  crescent. 


FIG.  193. — SECTION  OF  PART  OF  THE  HUMAN  SUBM AXILLARY  GLAND.     (Heidenhain.) 

To  the  right  of  the  figure  is  a  group  of  mucous  alveoli,  to  the  left  a  group  of  serous  alveoli. 

The  cells  of  the  alveoli  differ  according  to  the  substance  they 
secrete.  In  alveoli  which  secrete  mucus,  such  as  all  the  alveoli  of  the 
dog's  submaxillary,  and  some  of  the  alveoli  of  the  same  gland  in  man 
(fig.  193),  the  cells,  if  examined  in  watery  solution  or  after  hardening 


104 


THE  ESSENTIALS  OF  HISTOLOGY. 


with  alcohol,  are  clear  and  swollen.  But  if  examined  rapidly  in  serum,, 
or  in  solutions  of  salt  of  from  2  to  5  per  cent.,  they  are  seen  to  be 
occupied  by  large  and  distinct  granules,  formed  of  a  substance  which  is- 
known  as  mucigen  (fig.  195,  a).  This  mucigen  is  dissolved  out  of  the 
cell  and  discharged  into  the  lumen  of  the  alveolus,  and  into  the  ducts- 
when  the  gland  is  stimulated  to  activity.  But  in  each  alveolus  there 
are  some  smaller  cells  which  do  not  contain  mucigen,  and  these  gener- 


FIG.  194. — ALVEOLI  OF  A  SEROUS  GLAND.     A,  AT  REST.     B,  AFTER  A  SHORT  PERIOD  OK 

ACTIVITY.      0,  AFTER  A  PROLONGED  PERIOD  OF  ACTIVITY.      (Lailgley. ) 
In  A  and  B  the  nuclei  are  obscured  by  the  granules  of  zyniogen. 

ally  form  crescentic  groups  which  lie  next  to  the  basement-membrane 
(fig.  192,  c).  These  are  the  so-called  crescents  of  Gianuzzi ;  their  con- 
stituent cells  are  known  also  as  marginal  cells.  In  alveoli,  on  the  other 


FIG.  195.— Mucous  CELLS  FROM  FRESH  SUBMAXILLARY  GLANDS  OF  THE  DOG.     (Langley.) 

a,  from  a  resting  or  loaded  gland  ;  b,  from  a  gland  which  has  been  secreting  for  some  time  ; 
a',  b',  similar  cells  which  have  been  treated  with  dilute  acid. 

hand,  which  do  not  secrete  mucus,  but  watery  or  serous  saliva,  such  as 
the  parotid  in  all  animals,  and  some  of  the  alveoli  of  the  human  sub- 
maxillary,  the  cells  are  filled  with  small  granules  when  the  gland  is  at 
rest,  which  do  not  swell  with  water  nor  form  mucin ;  they  appear  to  be 


THE  SALIVARY  GLANDS. 


10.") 


albuminous  in  nature,  and  probably  yield  to  the  secretion  of  the 
inland  its  ferment  (ptyalin)  and  perhaps  its  albumin.  The  granular 
substance  within  the  cell  is  not  the  ferment,  but  the  ferment  is  formed 
from  it  when  the  secretion  is  poured  out.  Hence  it  has  been  termed 
'.'t/uwyrn  (mother  of  ferment).  The  outer  part  of  each  cell  becomes 
•clear  and  free  from  granules  after  secretion  (fig.  194). 

The  largest  ducts  have  a  wall  of  connective  tissue  outside  the  base- 
ment-membrane, and  also  a  few  plain  muscular  cells.  The  blood-vessels 
of  the  salivary  gland  form  a  capillary  network  around  each  alveolus. 
The  lymphatics  commence  in  the  form  of  lacunar  vessels  encircling  the 
.alveoli.  The  nerve-fibres,  which  are  derived  both  from  the  cerebro- 
spinal  nerves  and  from  the  sympathetic,  have  not  been  satisfactorily 
traced  to  their  termination,  but  they  probably  become  connected  with 
the  alveolar  cells. 

THE  PHARYNX  AND  (ESOPHAGUS. 

The  pharynx  is  composed  of  a  fibrous  membrane,  which  is  encircled 
by  striated  muscles,  the  constrictors,  and  lined  by  mucous  membrane. 
The  mucous  membrane  is  lined  in  the  upper  part  of  the  pharynx  and 


FIG.  196.— SECTION  OF  THE  HUMAN  (ESOPHAGUS.     (From  a  sketch  by  V.  Horsley.) 

The  section  is  transverse,  and  from  near  the  middle  of  the  gullet,  a,  fibrous  covering ;  b, 
divided  fibres  of  the  longitudinal  muscular  coat ;  c,  transverse  muscular  fibres  ;  d,  sub- 
mucous  or  areolar  layer;  e,  muscularis  mucosse  ;  /,  papillae  of  mucous  membrane  ;  g,  lami- 
nated epithelial  lining  ;  h,  mucous  gland ;  i,  gland  duct ;  m',  striated  muscular  fibres  in 
section. 


166  THE  ESSENTIALS  OF  HISTOLOGY. 

on  the  upper  surface  of  the  soft  palate  with  ciliated  epithelium,  which 
is  continuous  with  that  of  the  nostrils,  and  through  the  Eustachian 
tube  with  that  of  the  tympanum.  Below  the  level  of  the  soft  palate 
the  epithelium  is  stratified  like  that  of  the  mouth  and  gullet,  into 
which  it  passes.  In  certain  parts  the  mucous  membrane  contains  a 
large  amount  of  lymphoid  tissue,  especially  at  the  back,  where  it 
forms  a  projection  which  is  sometimes  termed  the  pharyngeal  tonsil, 
and  there  are  numerous  mucous  glands  opening  on  its  surface. 

The  oesophagus  or  gullet,  which  passes  from  the  pharynx  to  the 
stomach,  consists,  like  the  pharynx,  of  a  jibrom  covering,  a  muscular 
wat,  a  lining  mucous  membrane,  and  intervening  connective  tissue 
(areolar  coat)  (fig.  196).  The  muscular  coat  is  much  more  regularly 
arranged  than  that  of  the  pharynx,  and  is  composed  of  striated  muscle 
in  about  its  upper  third  only,  the  rest  being  of  the  plain  variety.  There 
are  two  layers  of  the  muscular  coat,  an  outer  layer,  in  which  the  fibres 
run  longitudinally,  and  an  inner,  in  which  they  course  circularly.  The 
mucous  membrane  is  lined  by  a  stratified  epithelium,  into  which  micro- 
scopic papilla?  from  the  corium  project.  The  corium  is  formed  of  areolar 
tissue,  and  its  limits  are  marked  externally  by  a  narrow  layer  of  longi- 
tudinally disposed  plain  muscular  fibres,  the  muscularis  mucosce.  This 
is  separated  from  the  proper  muscular  coat  by  the  areolar  coat,  which 
contains  the  larger  branches  of  the  blood-vessels  and  lymphatics,  and 
also  most  of  the  mucous  glands  of  the  membrane. 


THE  STRUCTURE  OF  THE  STOMACH.  167 


LESSON  XXX. 


THE  STRUCTURE  OF  THE  STOMACH. 

1.  SECTIONS  of  the  cardiac  region  of  the  dog's  stomach,  cut  perpendicularly 
to  the  surface  of  the  mucous  membrane.  The  tissue  is  stained  with  hgema- 
toxylin  or  carmine,  and  the  sections  are  mounted  in  Canada  balsam. 

In  these  sections  the  general  arrangement  of  the  coats  of  the  stomach  is  to 
be  studied,  and  sketches  are  to  be  made  under  a  low  power  illustrating  this 
arrangement,  and  others  under  a  high  power  showing  the  structure  of  the 
glands  of  the  mucous  membrane. 

Measure  the  whole,  thickness  of  the  mucous  membrane,  the  thickness  of  the 
muscular  coat,  the  size  of  the  columnar  epithelium-cells  of  the  surface,  and 
that  of  the  cells  in  the  deeper  parts  of  the  glands. 

2.  Sections  of  the  mucous  membrane  of  the  same  region,  cut  parallel  to 
the  surface. 

These  sections  will  show  better  than  the  others  the  arrangement  of  the 
cells  in  the  glands. 

3.  Vertical  sections  of  the  mucous  membrane  from  the  pyloric  region  of  the 
dog's  stomach.     If  the  section  is  taken  longitudinally  through  the  pylorus 
the  transition  of  the  gastric  glands  into  the  glands  of  Brumier  of  the  duo- 
denum will  be  made  manifest.     Make  a  sketch  under  a  low  power  of  one  of 
the  glands  in  its  whole  length,  filling  up  some  of  the  details  with  the  high 
power. 

4.  Study  the  arrangement  of  the  blood-vessels  of  the  stomach  in  vertical 
sections  of  the  wall  of  an  organ  the  vessels  of  which  have  been  injected. 


The  wall  of  the  stomach  consists  of  four  coats,  which,  enumerated 
from  without  in,  are  as  follows,  viz.  :  serous,  muscular,  areolar  or  sub- 
mucous,  and  mucous  membrane. 

The  serous  coat  is  a  layer  which  is  derived  from  the  peritoneum.  It 
is  deficient  only  along  the  lines  of  the  lesser  and  greater  curvatures. 

The  muscular  coat  consists  of  three  layers  of  plain  muscular  fibres. 
Of  these  the  bundles  of  the  outer  layer  run  longitudinally,  those  of  the 
middle  layer  circularly,  and  those  of  the  inner  layer  obliquely.  The 
longitudinal  and  circular  bundles  become  thicker  and  stronger  towards 
the  pylorus,  at  which  they  pass  into  the  corresponding  layers  of  the 
small  intestine ;  at  the  pylorus  itself  the  circular  layer  is  greatly 
thickened  to  form  the  sphincter  muscle.  The  oblique  fibres  are  only 
present  in  the  left  or  cardiac  part  of  the  stomach. 

The  areolar  or  submucous  coat  is  a  layer  of  areolar  tissue,  which  serves 
to  unite  the  mucous  membrane  loosely  to  the  muscular  coat ;  in  it 
ramify  the  larger  branches  of  the  blood-vessels  and  lymphatics. 


168 


THE  ESSENTIALS  OF  HISTOLOGY. 


FlG.  198.— A  CARDIAC  GLAND   OF 
DIMPLE  FORM,  FROM  THE  BAT's 

STOMACH.  (Osmic  acid  prepara- 
tion. )    ( Langley . ) 
c,   columnar  epithelium  of  the  sur- 
face ;  n,  neck  of  the  gland  with 
central  and  parietal-cells  ;  /,  base 
or    fundus,    occupied    only    by 
principal  or  central  cells,  which 
exhibit  the  granules  accumulated 
towards  the  lumen  of  the  gland. 


FIG.  197.— A  CARDIAC  GLAND  FROM  THE  DOG'S  STOMACH.     (Highly  magnified.)     (Klein.) 

d,  duct  or  mouth  of  the  gland  ;  b,  base  or  fundus  of  one  of  its  tubules.     On  the  right  the  base 

of  a  tubule  more  highly  magnified  ;  c,  central  cell ;  p,  parietal  cell. 


THE  STRUCTURE  OF  THE  STOMACH. 


169 


The  mucous  membrane  is  a  soft,  thick  layer,  generally  somewhat 
corrugated  in  the  empty  condition  of  the  organ.  Its  thickness  is 
mainly  due  to  the  fact  that  it  is  largely  made  up  of  long  tubular  glands, 
which  open  upon  the  inner  surface.  Between  the  glands  the  mucous 
membrane  is  formed  of  areolar  with  much  lymphoid  tissue.  Externally 
it  is  bounded  by  the  muscularis  mucosw,  which  consists  of  an  external 
longitudinal  and  an  inner  circular  layer  of  plain  muscular  fibres.  The 
glands  are  formed  of  a  basement-membrane  lined  with  epithelium. 
Each  gland  consists  of  three  or  four  secreting  tubules,  which  open 
towards  the  surface  into  a  larger  common  tube,  the  duct  of  the  gland. 
The  duct  is  in  all  cases  lined  by  columnar  epithelium  of  the  same 
character  as  that  which  covers  the  inner  surface  of  the  mucous  mem- 
brane, but  the  epithelium  of  the  secreting  tubules  is  different  from 
this,  and  also  differs  somewhat  in  the  glands  of  the  cardiac  and  pyloric 
regions  of  the  organ. 


FIG.  199.— SECTION  OF  THE  GASTRIC  MUCOUS  MEMBRANE  TAKEN  ACROSS  THE 
DIRECTION  OF  THE  GLANDS  (CARDIAC  PART). 

6,  basement  membrane  ;  c,  central  cells  ;  o,  oxyntic  cells  ;  ?•,  retiform  tissue  (with 
sections  of  blood-capillaries)  between  the  glands. 

• 

In  the  cardiac  glands  (fig.  197)  the  secreting  tubules  are  long,  and 
the  duct  short.  The  epithelium  of  the  tubules  is  composed  of  two  kinds 
of  cells.  Those  of  the  one  kind,  which  form  a  continuous  lining  to  the 
tubule,  are  somewhat  polyhedral  in  shape,  and  in  stained  sections  look 
clearer  and  smaller  than  the  others,  but  in  the  fresh  glands,  and  in 
osmic  preparations,  they  appear  filled  with  granules  (fig.  198).1  These 
cells  are  believed  to  secrete  the  pepsin  of  the  gastric  juice,  and  are 

lfrhe  granules  are  most  numerous  at  the  inner  part  of  the  cell,  a  small  outer 
zone  being  left  clear.  After  prolonged  activity  this  outer  zone  increases  in  size 
while  the  granules  diminish  in  number  as  in  the  analogous  cases  of  the  pancreas 
and  parotid  glands. 


170 


THE  ESSENTIALS  OF  HISTOLOGY. 


termed  the  chief  cell*  of  the  cardiac  glands,  or,  from  their  relative 
position  in  the  tubule  immediately  surrounding  the  lumen,  the  central 
cells.  Scattered  along  the  tubule,  and  lying  between  the  chief  cells 
and  the  basement-membrane,  are  a  number  of  other  spheroidal  or 
ovoidal  cells,  which  become  stained  by  logwood  and  other  reagents 
more  darkly  than  the  central  cells.  These  are  the  superadded  or 
parietal  cells  (oxi/ntic  cells1  of  Langley).  Each  parietal  cell  is  surrounded 


FlG.  200.  —  A  CARDIAC  GLAND 
PREPARED  BY  GOLGl'S  METHOD, 
SHOWING  THE  MODE  OF  COM- 
MUNICATION OP  THE  PARIETAL 
CELLS  WITH  THE  GLAND-LUMEN. 

(E.  Midler.) 


FlG.    201. — A   PYLORIC    GLAND, 
FROM     A     SECTION     OF      THE 

DOG'S  STOMACH.     (Ebstein.) 

m,  mouth  ;  n,  neck  ;  tr,  a  deep  por- 
tion of  a  tubule  cut  transversely. 


by  a  network  of  fine  passages,  communicating  with  the  lumen  of  the 

gland  by  a  fine  canal,  which  passes  between  the  central  cells  (fig.  200). 

In  the  pyloric  glands  (fig.  201)  the  ducts  are  much  longer  than  in 

the  cardiac  glands,  and  the  secreting  tubules  possess  cells  of  only  one 

1  So  called  because  they  produce  the  acid  of  the  gastric  secretion. 


THE  STRUCTURE  OF  THE  STOMACH. 


17T 


kind.1  These  correspond  to  the  chief  cells  of  the  cardiac  glands. 
They  are  of  a  columnar  or  cubical  shape,  and  in  the  fresh  condition 
of  a  granular  appearance,  and  quite  unlike  the  columnar  epithelium- 
cells  of  the  surface,  which  are  long  tapering  cells,  the  outer  part  of 
which  is  filled  with  mucus. 

At  the  pylorus  itself  the  glands  become  considerably  lengthened,, 
and  are  continued  into  the  submucous  tissue,  the  muscularis  mucosse 
being  here  absent ;  they  thus  present  transitions  to  the  glands  of 
Brunner,  which  lie  in  the  submucous  tissue  of  the  duodenum,  and 
send  their  ducts  through  the  mucous  membrane  to  the  inner  surface. 


FIG.  202,  A.— PLAN  OF  THE  BLOOD- 
VESSELS OF  THE  STOMACH. 
(Modified  from  Brinton.) 

«,  small  arteries  passing  to  break  up 
into  the  fine  capillary  network,  d, 
between  the  glands;  b,  coarser 
capillary  network  around  the 
mouths  of  the  glands ;  c,  c,  veins 
passing  vertically  downwards  from 
the  superficial  network ;  e,  larger 
vessels  in  the  submucosa. 


FIG.  202,  B. — LYMPHATICS  OF  THE  HUMAN  GASTRIC 

MUCOUS   MEMBRANE,    INJECTED.      (C.    Loven.) 

The  tubules  are  only  faintly  indicated ;  a,  muscularis 
rnucosse ;  b,  plexus  of  fine  vessels  at  base  of  glands  ;  c, 
plexus  of  larger  valved  lymphatics  in  submucosa. 


The  Mood-vessels  of  the  stomach  are  very  numerous,  and  pass  to  the 
organ  along  its  curvatures.  The  arteries  pass  through  the  muscular 
coat,  giving  off  branches  to  the  capillary  network  of  the  muscular 
tissue,  and  ramify  in  the  areolar  coat.  From  this,  small  arteries 
pierce  the  muscularis  mucosa;,  and  break  up  into  capillaries  near  the 
bases  of  the  glands  (fig.  202,  A).  The  capillary  network  extends  between 
the  glands  to  the  surface,  close  to  which  it  terminates  in  a  plexus  of 
relatively  large  venous  capillaries  which  encircle  the  mouths  of  the 
glands.  From  this  plexus  straight  venous  radicles  pass  through  the 

1  In  man  it  is  only  quite  near  the  pylorus  that  the  parietal  cells  are  altogether 
absent. 


172  THE  ESSENTIALS  OF  HISTOLOGY. 

mucous  membrane,  pierce  the  muscularis  mucosae,  and  join  a  plexus  of 
veins  in  the  submucous  tissue.  From  these  veins  blood  is  carried 
away  from  the  stomach  by  efferent  veins,  which  accompany  the-  enter- 
ing arteries. 

The  lymphatics  (fig.  202,  B)  arise  in  the  mucous  membrane  by  a 
plexus  of  large  vessels  dilated  at  intervals,  and  looking  in  sections  like 
clefts  in  the  interglandular  tissue.  From  this  plexus  the  lymph  is 
carried  into  larger  valved  vessels  in  the  submucous  coat,  and  from 
these,  efferent  vessels  pass  through  the  muscular  coat  to  reach  the 
serous  membrane,  underneath  which  they  pass  away  from  the  organ. 
The  muscular  coat  has  its  own  network  of  lymphatic  vessels.  These 
lie  between  the  two  principal  layers,  and  their  lymph  is  poured  into 
the  efferent  lymphatics  of  the  organ. 

The  nerves  have  the  same  arrangement  and  mode  of  distribution 
as  those  of  the  small  intestine  (see  next  Lesson). 


STRUCTURE  OF  THE  INTESTINE.  173 


LESSONS  XXXI.  AND  XXXII. 

STRUCTURE  OF    THE   INTESTINE. 
LESSON  XXXI. 

1.  SECTIONS  of  the  duodenum  and  jejunum  vertical  to  the  surface.  The  tissue 
is  to  be  stained  with  hsematoxylin  and  the  sections  mounted  in  Canada  balsam. 
The  general  arrangement  and  structure  of  the  intestinal  wall  is  to  be  studied 
in  these  sections. 

Make  a  general  sketch  under  the  low  power  and  carefully  sketch  part  of  a 
villus  under  the  high  power. 

•2.  Sections  parallel  to  the  surface  of  the  intestine,  and  therefore  across  the 
long  axis  of  the  villi  and  glands  of  the  mucous  membrane.  In  order  to  keep 
the  sections  of  the  villi  together  so  that  they  are  not  lost  in  the  mounting,  it 
is  necessary  either  to  embed  in  celloidin  or,  if  paraffin  be  used,  to  employ  an 
adhesive  method  of  mounting  (see  Appendix). 

In  this  preparation  sketch  the  transverse  section  of  a  villus  and  of  a  crypt 
of  Lieberkiilm. 

3.  Transverse  vertical  sections  of  the  ileum  passing  through  a  Peyer's  patch. 
Observe  the  nodules  of  lymphoid  tissue  which  constitute  the  patch  and  which 
extend  into  the  submucous  tissue.     Notice  also  the  sinus-like  lymphatic  or 
lacteal  vessel  which  encircles  the  base  of  each  nodule.    Make  a  general  sketch 
under  a  low  power. 

4.  To  study  the  process  of  fat-absorption,  kill  a  mammal,  e.g.  rat,  three  or 
four  hours  after  feeding  it  with  a  little  fat,  or  a  frog  two  or  three  days  after 
feeding  with  lard.     Put  a  very  small  shred  of  the  mucous  membrane  of  the 
intestine  into  osmic  acid  (0'5  per  cent.)  and  another  piece  into  a  mixture  of  2 
parts  Muller's  fluid  and   1   part  osmic  acid  solution  (1  per  cent.).     After 
forty-eight  hours  teased  preparations  may  be  made  from  the  osmic  acid 
preparation,  in  the  same  manner  as  directed  in  Lesson  VII.,  sec.  2  ;  the  rest 
may  be  then  placed  in  70  per  cent,  alcohol.     The  piece  in.  Miiller  and  osmic 
acid  may  be  left  for  ten  days  or  more  in  the  fluid.     When  hardened,  the 
pieces  of  tissue  are  soaked   in   gum,    and   sections   made  with   a   freezing 
microtome  and  mounted  in  glycerine.      The  sections  must  not  be  passed 
through  any  fluid  which  dissolves  fat. 


LESSON  XXXII. 

1.  SECTIONS  of  small  intestine  the  blood-vessels  of  which  have  been  injected. 
Notice  the  arrangement  of  the  vessels  in  the  several  layers.  Sketch  carefully 
the  vascular  network  of  a  villus. 

2.  From  a  piece  of  intestine  which  has  been  stained  with  chloride  of  gold 
tear  off  broad  strips  of  the  longitudinal  muscular  coat,  and  mount  them  in 
glycerine.  It  will  generally  be  found  that  portions  of  the  nervous  plexus  of 
Auerbach  remain  adherent  to  the  strips,  and  the  plexus  can  in  this  way  easily 
be  studied. 


174 


THE  ESSENTIALS  OF  HISTOLOGY. 


From  the  remainder  of  the  piece  of  intestine  tear  off  with  forceps  the  fibres 
of  the  circular  muscular  layer  on  the  one  side,  and  the  mucous  membrane  on 
the  other  side,  so  as  to  leave  only  the  submucous  tissue  and  the  muscularis 
mucosse.  This  tissue  is  also  to  be  mounted  flat  in  glycerine  :  it  contains  the 
plexus  of  Meissiier. 

Sketch  a  small  portion  of  each  plexus  under  a  high  power. 

3.  Sections  of  the  large  intestine,  perpendicular  to  the  surface.     These  will 
show  the  general  structure  and  arrangement  of  the  coats.     Sketch  under  a 
low  power. 

4.  Sections  of  the  mucous  membrane  of  the  large  intestine  parallel  to  the 
surface,  and  therefore  across  the  glands.     Sketch  some  of  the  glands  and  the 
interglandular  tissue  under  a  high  power. 

5.  The  arrangement  of  the  blood-vessels  of  the  large  intestine  may  be 
.studied  in  sections  of  the  injected  organ. 


THE  SMALL  INTESTINE. 

The  wall  of  the  small  intestine  consists,  like  the  stomach,  of  four  coats. 
The  serous  coat  is  complete  except  over  part  of  the  duodenum. 


FIG.  203. — PLEXUS  OF  AUERBACH,  BETWEEN  THE  TWO  LAYERS  OF  THE  MUSCULAR  COAT 

OF  THE  INTESTINE.      (Cadiat.) 

The  muscular  coat  is  composed  of  two  layers  of  muscular  tissue,  an 
outer  longitudinal  and  an  inner  circular.  Between  them  lies  a  net- 
work of  lymphatic  vessels  and  also  the  close  gangliated  plexus  of  non- 
medullated  nerve-fibres  known  as  the  plexus  myentericus  of  Auerbach. 
The  ganglia  of  this  plexus  may  usually  be  seen  in  vertical  sections  of 


STRUCTURE  OF  THE  INTESTINE. 


175 


the  intestinal  wall,  but  the  plexus,  like  the  one  in  the  submucous  coat 
immediately  to  be  described,  can  only  be  properly  displayed  in  prepara- 
tions made  with  chloride  of  gold  (fig.  203)  or  methyl-blue. 


FIG.  204. — PLEXUS  OK  MEISSNER  FROM  THE  SUBMUCOUS  COAT  OF  THE  INTESTINE. 

(Cadiat  ) 


FIG.  205. — CROSS-SECTION  OF  A  SMALL  FRAGMENT  OF  THE  MUCOUS  MEMBRANE  OF  THE 
INTESTINE,  INCLUDING  ONE  ENTIRE  CRYPT  OF  LIEBERKUHN  AND  PARTS  OF  THREE 
OTHERS.  (Magnified  400  diameters. )  (Frey.) 

«,  cavity  of  the  tubular  glands  or  crypts  ;  6,  one  of  the  lining  epithelial-cells  ;  c,  the 
interglandular  tissue  ;  d,  lymph-cells. 


176 


THE  ESSENTIALS  OF  HISTOLOGY. 


The  submucous  coat  is  like  that  of  the  stomach ;  in  it  the  blood- 
vessels and  lymphatics  ramify  before  entering  or  after  leaving  the 
mucous  membrane,  and  it  contains  a  gangliated  plexus  of  nerve-fibres — 


s 

FIG.  206.— SECTION  OF  THE  ILEUM  THROUGH  A  LYMPHOID  NODULE,    (Cadiat.) 

a,  middle  of  the  nodule  with  the  lymphoid  tissue  partly  fallen  away  from  the  section  ;  br 
epithelium  of  the  intestine  ;  c,  villi  :  their  epithelium  is  partly  broken  away ;  </,  crypts 
of  Lieberkiihn. 


FIG.  207.— CROSS-SECTION  OF  AN  INTESTINAL  VILLUS. 

e,  columnar  epithelium  ;  g,  goblet-cell,  its  mucus  is  seen  partly  extruded  ;  I,  lymph-corpuscles 
between  the  epithelium -cells  ;  b,  basement-membrane  ;  c,  blood-capillaries  ;  m,  section  ot 
plain  muscular  fibres  ;  c.l,  central  lacteal. 

the  plexus  of  Meissner — which  is  finer  than  that  of  Auerbach  and  has 
fewer  ganglion-cells  (fig.  204).  Its  branches  are  chiefly  supplied  to  the 
muscular  fibres  of  the  mucous  membrane. 


STEUCTUEE  OF  THE  INTESTINE. 


177 


The  mucous  membrane  is  bounded  next  to  the  submucous  coat  by  a 
double  layer  of  plain  muscular  fibres  (muscularis  mucosce).  Bundles 
from  this  pass  inwards  through  the 
membrane  towards  its  inner  surface 
and  penetrate  also  into  the  villi. 
The  mucous  membrane  proper  is 
pervaded  with  simple  tubular  glands 
— the  crypts  of  Lieberkulm — which 
are  lined  throughout  by  a  colum- 
nar epithelium  like  that  which 
covers  the  surface  and  the  villi. 
The  mucous  membrane  between 
these  glands  is  mainly  composed  of 
lymphoid  tissue,  which  is  aggre- 
gated at  intervals  into  more  solid 
nodules  (fig.  206),  constituting  when 
they  occur  singly  the  so-called  soli- 
tary glands  of  the  intestine,  and 
when  aggregated  together  form  the 
agminated  glands  or  patches  of  Peyer. 
The  latter  occur  chiefly  in  the  ileum. 

The  villi  with  which  the  whole 
of  the  inner  surface  of  the  small 
intestine  is  closely  beset  are  clavate 
or  finger-shaped  projections  of  the 
mucous  membrane,  and  are  com- 
posed, like  that,  of  lymphoid  tissue 
arid  covered  with  columnar  epi- 
thelium (fig.  207).  The  characters 
of  this  have  been  already  described 
(Lesson  VII.).  Between  and  at 
the  base  of  the  epithelium-cells 
many  lymph-corpuscles  occur.  The 
epithelium  rests  upon  a  basement- 
membrane  formed  of  flattened  cells. 
In  the  middle  of  the  villus  is  a 
lacteal  vessel  (c.L)  which  is  some- 
what enlarged  near  its  commencement.  It  is  replaced  in  some  animals 
by  a  network  of  lymphatics.  Surrounding  this  vessel  are  small  bundles 
of  plain  muscular  tissue  prolonged  from  the  muscularis  mucosa3.  The 
network  of  blood-capillaries  (fig.  208)  lies  for  the  most  part  near  the 
surface  within  the  basement-membrane ;  it  is  supplied  with  blood  by 


FIG.  208. — SMALL  INTESTINE,  VERTICAL 

TRANSVERSE       SECTION       WITH       THE 
BLOOD-VESSELS     INJECTED.          (Heitz- 

mann. ) 

V,  a  villus ;  G,  glands  of  Lieberktihn ;  M, 
muscularis  mucosae ;  A,  areolar  coat;  R, 
ring-muscle  (circular  layer  of  muscular 
coat) ;  L,  longitudinal  layer  'of  muscular 
coat ;  p,  peritoneal  coat. 


178 


THE  ESSENTIALS  OF  HISTOLOGY. 


a  small  artery  which  joins  the  capillary  network  at  the  base  of  the 
villus  ;  the  corresponding  vein  generally  arises  nearer  the  extremity. 

The  lymphatics  (lacteals)  of  the  mucous  membrane  (fig.  209),  after 
receiving  the  central  lacteals  of  the  villi,  pour  their  contents  into  a 
plexus  of  large  valved  lymphatics  which  lie  in  the  submucous  tissue 
and  form  sinuses  around  the  bases  of  the  lymphoid  nodules.  From 
the  submucous  tissue  efferent  vessels  pass  through  the  muscular  coat, 
receiving  the  lymph  from  an  intramuscular  plexus  of  lymphatics,  and 
are  conveyed  away  between  the  layers  of  the  mesentery. 


FIG.  209. — VERTICAL  SECTION  OF  A  PORTION  OF  A  PATCH  OF  PETER'S  GLANDS  WITH 

THE  LACTEAL  VESSELS  INJECTED.     (32  diameters. )     (Frey. ) 

The  specimen  is  from  the  lower  part  of  the  ileum  :  a,  villi,  with  their  lacteals  left  white ; 
b,  some  of  the  tubular  glands ;  c,  the  muscular  layer  of  the  mucous  membrane  ;  d,  cupola 
or  projecting  part  of  the  nodule  ;  e,  central  part ;  /,  the  reticulated  lacteal  vessels  occu- 

the 


Absorption  of  fat. — The  lymph-corpuscles  of  the  villi  are  in  some 
animals — e.g.  rat,  frog — important  agents  in  effecting  the  passage  of  fat- 
particles  into  the  lacteals.  In  other  animals  much  of  the  fat  is  absorbed 
in  the  form  of  soap,  and  takes  a  fluid  form  in  its  passage  into  the  lacteals 
of  the  villi.  In  order  to  study  the  process  of  transference,  it  is  con- 
venient to  stain  the  fat  with  osmic  acid,  which  colours  it  black.  It 
can  then  be  observed  that  in  animals  of  the  former  category  which 
have  been  fed  with  fat  these  particles  are  present  (1)  in  the  columnar 
epithelium-cells  ;  (2)  in  the  lymph-cells  ;  and  (3)  in  the  central  lacteal 
of  the  villus.  The  lymph-cells  are  present  not  only  in  the  reticular 
tissue  of  the  villus,  but  also  in  considerable  number  between  the 
epithelium-cells  ;  and  they  can  also  be  seen  in  thin  sections  from  osmic 
preparation  within  the  commencing  lacteal ;  but  in  the  last  situation 
they  are  undergoing  disintegration. 


STRUCTURE  OF  THE  INTESTINE. 


171) 


Since  the  lymph-cells  are  amoeboid,  it  is  probable  from  these  facts 
that  the  mechanism  of  fat  absorption  in  these  cases  consists  of  the  fol- 
lowing processes — viz.  (1)  absorption  of  fat  into  the  columnar  epi- 
thelium-cells of  the  surface ;  (2)  inception  of  fat  by  the  lymph- 
corpuscles  in  the  epithelium,  these  taking  it  up  after  it  has  passed — 
through  the  epithelium-cells ;  (3)  migration  of  the  lymph -corpuscles 
carrying  the  incepted  fat-particles  by  their  amoeboid  movements 
through  the  tissue  of  the  villus  and  into  the  central  lacteal ;  (4) 
disintegration  and  solution  of  the  immigrated  lymph-corpuscles,  and 
setting  free  both  of  their  fatty  contents  and  also  of  the  proteid  matters 
of  which  they  are  themselves  composed. 

This  migration  of  the  lymph-corpuscles  into  the  lacteals  of  the  villi 
is  not  a  special  feature  of  fat-absorption  alone,  but  occurs  even  when 
A 


sir 


cp 


FIG.  210. — SECTION  OF  THE  VILLUS  OF  A  RAT  KILLED  DURING  FAT- ABSORPTION. 

ep,  epithelium  ;  sir,  striated  border;  c,  lymph-cells  :  c',  lymph-cells  .in  the  epithelium; 
I,  central  lacteal  containing  disintegrating  lymph-corpuscles. 

FIG.  211. — Mucous  MEMBRANE  OF  FROG'S  INTESTINE  DURING  FAT- ABSORPTION. 
ep,  epithelium  ;  str,  striated  border  ;  c,  lymph-corpsucles  ;  I,  lacteal. 

•absorption  of  other  matters  is  proceeding ;  so  that  the  'transference  of 
fat-particles  is  merely  a  part  of  a  more  general  phenomenon  accompany- 
ing absorption. 

THE  LARGE  INTESTINE. 

The  large  intestine  has  the  usual  four  coats,  except  near  its  termina- 
tion, where  the  serous  coat  is  absent.     The  muscular  coat  is  peculiar  in 


180 


THE  ESSENTIALS  OF  HISTOLOGY. 


the  fact  that  along  the  caecum  and  colon  the  longitudinal  muscular 
fibres  are  gathered  up  into  three  thickened  bands  which  produce 
puckerings  in  the  wall  of  the  gut. 

The  mucous  membrane  of  the  large  intestine  is  beset  with  simple 
tubular  glands  somewhat  resembling  the  crypts  of  Lieberkiihn  of  the 
small  intestine,  and  lined  by  columnar  epithelium  similar  to  that  of  the 
inner  surface  of  the  gut,  but  containing  many  more  mucus-secreting  or 
goblet  cells  (fig.  212).  The  extremity  of  each  gland  is  usually  slightly 
dilated.  The  interglandular  tissue  is  like  that  of  the  stomach,  as  is 


FlG.  212.— A   GLAND  OF  THE  LARGE 
INTESTINE   OF  THE  DOG.      (From 

Heidenhain  and  Klose.) 

b,  in  longitudinal ;  c,  in  transverse 
section. 


also  the  arrangement  of  the  blood-vessels  and  lymphatics  in  it.  The 
nerves  of  the  large  intestine  also  resemble  those  of  the  small  intestine 
and  stomach  in  their  arrangement. 

At  the  lower  end  of  the  rectum  the  circular  muscular  fibres  of  the 
gut  become  thickened  a  little  above  the  anus  so  as  to  form  the  internal 
sphincter  muscle.  In  this  region  also  there  are  a  number  of  compound 
racemose  mucous  glands  opening  on  to  the  surface  of  the  mucous 
membrane  (anal  glands}. 


STEUCTURE  OF  THE  LIVEE.  181 


LESSON  XXXIII. 


STRUCTURE  OF  THE  LIVER  AND  PANCREAS. 

1.  MAKE  sections  of  liver,  pig's  and  human,  from  pieces  hardened  in  Mailer's 
fluid,  and  study  them  carefully  with  a  low  and  high  power.  Sketch  the 
general  arrangement  of  the  cells  in  a  lobule  under  the  low  power  and  under 
the  high  power.  Make  very  careful  drawings  of  some  of  the  hepatic  cells 
and  also  of  a  portal  canal. 

2.  To  observe  the  glycogen  and  the  iron-containing  pigment  within  the 
liver-cells,  kill  a  rabbit  (for  glycogen  preferably  about  six  hours  after  a  full 
meal  of  carrots),  and  at  once  throw  a  thin  piece  of  the  liver  into  90  per 
cent,  alcohol.     When  well  hardened  the  piece  may  be  embedded  in  paraffin 
in  the  usual  way,  or  sections  may  be  cut  with  the  free  hand  without  embed- 
ding.    Some  of  the  sections  so  obtained  are  to  be  treated  with  a  solution  of 
iodine  in  potassic  iodide  :  then  rapidly  dehydrated  by  alcohol  and  passed  into 
clove-oil.    They  may  now  be  mounted  in  Canada  balsam  solution.    These  will 
exhibit  the  glycogen  within  the  liver-cells.     Other  sections  are  to  be  treated 
first  with  potassic  ferrocyanide  solution  and  then  with  hydrochloric  acid  :  in 
these  many  of  the  pigment-granules  will  be  stained  blue  (presence  of  iron). 

3.  Study,  first  of  all  with  the  low  and  afterwards  with  a  high  power,  a 
section  of  the  liver  in  which  both  the  blood-vessels  and  the  bile  ducts  have 
been  injected.1     Make  a  general  sketch  of  a  lobule  under  the  low  power  and 
draw  a  small  part  of  the  network  of  bile-canaliculi  under  the  high  power. 

4.  Tease  a  piece  of  fresh  liver  in  serum  or  salt  solution  for  the  study  of  the 
appearance  of  the  hepatic  cells  in  the  recent  living  condition. 

5.  Stained  sections  of  pancreas  from  a  gland  which  has  been  hardened  in 
alcohol.     Small  pieces  of  the  gland  are  stained  in  bulk  and  the  sections 
mounted  in  the  usual  way  in  Canada  balsam. 

Make  a  sketch  under  the  low  power. 

6.  Tease  a  small  piece  of  fresh  pancreas  in  serum  or  salt  solution.     Notice 
the  granules  in  the  alveolar  cells,  chiefly  accumulated  in  the  half  of  the  cell 
which  is  nearest  the  lumen  of  the  alveolus,  leaving  the  outer  zone  of  the  cell 
clear. 

Sketch  a  small  portion  of  an  alveolus  under  a  high  power. 


THE  LIVER. 

The  liver  is  a  solid  glandular  mass,  made  up  of  the  hepatic  lobules. 
These  are  polyhedral  masses  about  1  mm.  (-^  inch)  in  diameter, 
composed  of  cells,  and  separated  from  one  another  by  connective  tissue. 

1  For  the  method  of  injecting  these,  see  Course  of  Practical  Histology.  They  can  also 
be  demonstrated  in  sections  of  liver  which  have  been  prepared  by  Golgi's  method  (see 
Appendix). 


182 


THE  ESSENTIALS  OF  HISTOLOGY. 


In  some  animals,  as  in  the  pig,  this  separation  is  complete,  and  each 
lobule  is  isolated,  but  in  man  it  is  incomplete.  There  is  also  a  layer 
of  connective  tissue  underneath  the  serous  covering  of  the  liver,  and 
forming  the  so-called  capsule  of  the  organ. 


FIG.  213. — SECTION  OF  A  POKTAL  CANAL. 

«,  branch  of  hepatic  artery  ;  v,  branch  of  portal  vein  ;  d,  bile-duct ;  /,  /,  lymphatics  in  the 
areolar  tissue  of  Glisson's  capsule  which  incloses  the  vessels. 


FIG.  214.— DIAGRAMMATIC  REPRESENTATION  OF  TWO  HEPATIC  LOBULES. 

The  left-hand  lobule  is  represented  with  the  intralobular  vein  cut  across  ;  in  the  right-hand 
one  the  section  takes  the  course  of  the  intralobular  vein,  p,  interlobular  branches  of  the 
portal  vein  ;  h,  intralobular  branches  of  the  hepatic  veins  ;  s,  sublobular  vein  ;  c,  capil- 
laries of  the  lobules.  The  arrows  indicate  the  direction  of  the  course  of  the  blood.  The 
liver-cells  are  only  represented  in  one  part  of  each  lobule. 

The  blood-vessels  of  the  liver  (portal  vein  and  hepatic  artery)  enter  it 
on  its  under  surface,  where  also  the  bile-duct  passes  away  from  the 
gland.  The  branches  of  these  three  vessels  accompany  one  another 
in  their  course  through  the  organ,  and  are  inclosed  by  loose  connec- 
tive tissue  (capsule  of  Glisson),  in  which  are  lymphatic  vessels,  the 


STRUCTURE  OF  THE  LIVER 


183 


whole  being  termed  a  portal  canal  (fig.  213).  The  smallest  branches 
of  the  vessels  penetrate  to  the  intervals  between  the  hepatic  lobules, 
and  are  known  as  the  interlobular  branches.  The  blood  leaves  the 
liver  at  the  back  of  the  organ  by  the  hepatic  veins  :  the  branches  of 
these  run  through  the  gland  unaccompanied  by  other  vessels  (except 


FIG.  215.— HEPATIC-CELLS  STILL  CONTAINING  GLYCOGEN,  a,  AND  WITH  THEIR 
GLYCOGEN  DISSOLVED  OUT,  6,  c.     (Heidenhain.) 

In  c  there  was  less  glycogen  present  than  in  b. 


FIG.  216. — SECTION  OF  BABBIT'S  LIVER  WITH  THE  INTERCELLULAR  NETWORK  OF  BILE- 
CANALICULI  INJECTED.     (Highly  magnified. )     (Hering.) 

Two  or  three  layers  of  cells  are  represented  ;  b,  b,  blood-capillaries. 

lymphatics)  and  can  also  be  traced  to  the  lobules,  from  each  of  which 
they  receive  a  minute  branch  (intralobular  vein)  which  passes  from  the 
centre  of  the  lobule,  and  opens  directly  into  the  (sublobular)  branch  of 
the  hepatic  vein. 


184 


THE  ESSENTIALS  OF  HISTOLOGY. 


Each  lobule  is  a  mass  of  hepatic  cells  pierced  everywhere  with  a 
network  of  blood-capillaries  (fig.  214),  which  arise  at  the  periphery  of 
the  lobule,  there  receiving  blood  from  the  interlobular  branches  of  the 
portal  vein  (p\  and  converge  to  the  centre  of  the  lobule,  where  they 
unite  to  form  the  intralobular  branch  of  the  hepatic  vein.  The  inter- 
lobular branches  of  the  hepatic  arteries  join  this  capillary  network  a 
short  distance  from  the  periphery  of  the  lobule. 


FIG.  217. — LOBULE  OF  BABBIT'S  LIVER,  VESSELS  AND  BILE-DUCTS  INJECTED.    (Cadiat. 
a,  central  vein  ;  b,  b,  peripheral  or  interlobular  veins  ;  c,  interlobular  bile-duct. 

The  hepatic  cells  (figs.  215,  216),  which  everywhere  lie  between  and 
surround  the  capillaries,  are  polyhedral,  somewhat  granular-looking  cells, 
each  containing  a  spherical  nucleus.  After  a  meal  the  cells  in  the 
outer  part  of  the  lobule  may  contain  fat  in  some  animals,  and  masses  of 
glycogen  can  also  be  seen  within  the  cells  if  the  liver  be  hardened  in 


STRUCTURE  OF  THE  PANCREAS.  185 

alcohol  and  treated  in  the  manner  described  in  section  2.  The  cells 
also  contain  pigment-granules,  many  of  which  are  stained  by  potassic 
ferrocyanide  and  hydric  chloride  (presence  of  iron). 

The  bile-ducts  commence  between  the  hepatic  cells  in  the  form  of  fine 
canaliculi,  which  lie  between  the  adjacent  sides  of  two  cells,  and  form  a 
close  network,  the  meshes  of  which  correspond  in  size  to  the  cells  (fig. 
216).  At  the  periphery  of  the  lobule  these  fine  canaliculi  pass  into  the 
interlobular  bile-ducts  (fig.  217). 

The  bile-ducts  are  lined  by  clear  columnar  epithelium  (fig.  214,  d). 
Outside  this  is  a  basement-membrane,  and  in  the  larger  ducts  some 
fibrous  and  plain  muscular  tissue.  Many  of  the  larger  ducts  are  beset 
with  small  csecal  diverticula. 

The  gall-bladder  is  in  its  general  structure  similar  to  the  larger  bile- 
ducts.  It  is  lined  by  columnar  epithelium,  and  its  wall  is  formed  of 
fibrous  and  muscular  tissue. 

The  lymphatics  of  the  liver  are  said  to  commence  as  perivascular 
lymphatic  spaces  inclosing  the  capillaries  of  the  lobules.  Efferent 
lymphatics  pass  away  from  the  organ  in  the  connective  tissue  which  in- 
vests the  portal  and  hepatic  veins. 

THE  PANCREAS. 

The  pancreas  is  a  tubulo-racemose  gland,  resembling  the  salivary 
glands,  so  far  as  its  general  structure  is  concerned,  but  differing  from 
them  in  the  fact  that  the  alveoli,  in  place  of  being  saccular,  are  longer 


FIG.  218.— SECTION  OF  THE  PANCREAS  OF  THE  DOG.    (Klein.) 
d,  termination  of  a  duct  in  the  tubular  alveoli,  alv. 

and  more  tubular  in  character  (fig.  218).  Moreover,  the  connective 
tissue  of  the  gland  is  somewhat  looser,  and  there  occur  in  it  at  intervals 
small  groups  of  epithelium -like  cells,  which  are  supplied  with  a  close 


186 


THE  ESSENTIALS  OP  HISTOLOGY. 


network  of  convoluted  capillary  vessels  ;  their  function  is  unknown,  but 
their  presence  is  very  characteristic  of  the  pancreas. 

The  cells  which  line  the  alveoli  are  columnar  or  polyhedral  in 
shape.  When  examined  in  the  fresh  condition,  or  in  osmic  prepara- 
tions, their  protoplasm  is  filled  in  the  inner  two-thirds  with  small 
granules,  but  the  outer  third  is  left  clear  (fig.  219,  A).  After  a  period 


FIG.  219.— PART  OF  AN  ALVEOLUS  OF  THE  RABBIT'S  PANCREAS.    A,  AT  REST  ; 
£,  AFTER  ACTIVE  SECRETION.     (From  Foster,  after  Kiihne  and  Lea.) 

a,  the  inner  granular  zone,  which  in  A  is  larger  and  more  closely  studded  with  fine  granules 
than  in  B,  in  which  the  granules  are  fewer  and  coarser ;  6,  the  outer  transparent  zone, 
small  in  A,  larger  in  B,  and  in  the  latter  marked  with  faint  strise  ;  c,  the  lumen,  very 
obvious  in  B,  but  indistinct  in  A  ;  d,  an  indentation  at  the  junction  of  two  cells,  only 
seen  in  B. 

of  activity  the  clear  part  of  the  cell  becomes  larger,  arid  the  granular 
part  smaller  (B\  In  stained  sections  the  outer  part  is  coloured  more 
deeply  than  the  inner. 

In  the  centre  of  each  acinus  there  may  generally  be  seen  some 
spindle-shaped  cells,  the  nature  of  which  (whether  epithelial  or  connec- 
tive tissue)  has  not  been  determined  (centro-acinar  cells  of  Langerhans). 


STRUCTTJBE  OF  THE  SPLEEN.  187 


LESSON  XXXIV. 

STRUCTURE  OF  THE  SPLEEN,  SUPRARENAL  CAPSULE,  AND 
THYROID  BODY. 

] .  SUCTIONS  of  the  spleen  stained  with  lueinatoxylin.  Notice  the  trabeculie 
extending  into  the  substance  of  the  organ  from  the  capsule.  Notice  also  that 
the  glandular  substance  is  of  two  kinds,  (1)  lymphoid  tissue  accumulated 
round  the  small  arteries  and  here  and  there  massed  to  form  lymphoid  nodules 
— the  Malpighian  corpuscles  of  the  spleen — and  (2)  a  tissue  consisting  of  a 
reticulum  of  branched  and  flattened  cells  containing  blood  in  its  interstices 
and  pervaded  by  capillaries  and  venous  radicles. 

Sketch  part  of  a  section  under  a  low  power  and  a  small  portion  of  the 
reticulum  under  a  high  power. 

•2.  Sections  across  a  suprarenal  capsule.  Examine  first  with  a  low  power, 
noticing  the  general  arrangement  and  extent  of  the  cortical  and  medullary 
parts  of  the  organ,  making  a  general  sketch  which  shall  include  both.  After- 
wards sketch  carefully  under  the  high  power  a  group  of  cells  from  each  part 
of  the  organ. 

3.  Sections  of  the  thyroid  body  stained  with  hsematoxylin.  Notice  the 
vesicles  lined  with  cubical  epithelium  and  filled  with  a  "  colloid  "  substance 
which  becomes  stained  by  the  haematoxylin.  Sketch  one  or  two  vesicles. 
Measure  several  vesicles. 


THE  SPLEEN. 

The  spleen  is  the  largest  of  the  so-called  ductless  glands.  It  appears 
to  be  functionally  connected  in  some  way  with  the  blood,  white  blood- 
corpuscles  being  certainly  formed  and  coloured  blood-corpuscles  being 
probably  submitted  to  destruction  within  it. 

Like  the  lymphatic  glands,  the  spleen  is  invested  with  a  fibrous  and 
muscular  capxule  (fig.  220,  A),  and  this  again  has  a  covering  derived 
from  the  serous  membrane.  The  capsule  sends  fibrous  bands  or  tra- 
beculse  (b)  into  the  organ,  and  these  join  with  a  network  of  similar 
trabeculse  which  pass  into  the  gland  at  the  hilurn  along  with  the  blood- 
vessels. In  the  interstices  of  the  fibrous  framework  thus  constituted 
lies  a  soft  pulpy  substance  containing  a  large  amount  of  blood,  and 
therefore  of  a  deep  red  colour,  dotted  within  which  are  here  and  there 
to  be  seen  small  whitish  specks,  the  Malpighian  cwpuscles  of  the  spleen 
(<;  r).  These  are  composed  of  lymphoid  tissue  which  is  gathered  up 


188 


THE  ESSENTIALS  OF  HISTOLOGY. 


into  masses  which  envelop  the  smaller  arteries,  whilst  the  red  pulp 
which  everywhere  surrounds  them  and  which  forms  the  bulk  of  the 
organ  is  composed  of  a  close  network  or  sponge  work  of  flattened  and 


FIG.  220. — VERTICAL  SECTION  OF  A  SMALL  SUPERFICIAL  PORTION  OF  THE  HUMAN 

SPLEEN,    AS   SEEN   WITH  A  LOW  POWER.       (Kolliker.) 

A,  peritoneal  and  fibrous  covering ;  b,  trabeculse ;  c,  c,  Malpighian  corpuscles,  in  one  of  -which 
an  artery  is  seen  cut  transversely,  in  the  other  longitudinally ;  d,  injected  arterial  twigs  ; 
e,  spleen-pulp. 


u. 


FIG.  221.— THIN  SECTION  OF  SPLEEN-PULP,  HIGHLY  MAGNIFIED,  SHOWING  THE 
MODE  OF  ORIGIN  OF  A  SMALL  VEIN  IN  THE  INTERSTICES  OF  THE  PULP. 

v,  the  vein,  filled  with  blood-corpuscles,  which  are  in  continuity  with  others,  bl,  filling  up  the 
interstices  of  the  retiform  tissue  of  the  pulp ;  -w,  wall  of  the  vein.  The  shaded  bodies 
amongst  the  red  blood-corpuscles  are  pale  corpuscles. 

branched  cells  like  connective-tissue  corpuscles.  Coursing  through  the 
pulp  and  communicating  with  its  interstices  are  capillary  blood-vessels 
which  are  connected  with  the  terminations  of  the  arteries ;  whilst  in 
other  parts  venous  channels  arise  from  the  pulp,  and  bring  the  blood 


STRUCTURE  OF  THE  SUPRARENAL  CAPSULES.  189- 

which  has  passed  into  its  interstices  from  the  arterial  capillaries 
towards  the  larger  veins  of  the  organ,  which  run  in  the  trabeculae,  and 
are  by  them  conducted  to  the  hilum.  The  arteries,  which  are  also  at 
first  conducted  from  the  hilum  along  the  trabeculse  into  the  interior  of 
the  organ,  presently  leave  the  trabeculss,  and  their  external  coat 
becomes  converted  into  a  thick  sheath  of  lymphoid  tissue  which  invests 
them  in  the  remainder  of  their  course,  and  in  places  becomes  swollen 
into  the  Malpighian  corpuscles  already  mentioned.  These  small 
arteries  distribute  a  few  capillaries  to  the  Malpighian  corpuscles,  and 
then  break  up  into  pencils  of  small  vessels  which  open  into  the  pulp  in: 
the  manner  before  described. 

The  cellular  elements  of  the  spleen-pulp  are  of  three  kinds,  viz. 
peculiar,  large,  amceboid  cells,  called  splenic  cells,  lymph-corpuscles,  and 
the  branched,  flattened  cells  which  form  the  sponge-work.  The  first- 
named  are  frequently  found  to  contain  coloured  blood-corpuscles  in 
their  interior  in  various  stages  of  transformation  into  pigment. 

The  lymphatics  of  the  spleen  run  partly  in  the  trabeculae  and  capsule,, 
and  partly  in  the  lymphoid  tissue  eiisheathing  the  arteries.  They  join 
to  form  larger  vessels  which  emerge  together  at  the  hilum. 

THE  SUPRARENAL  CAPSULES. 

The  suprarenal  capsules  belong  to  the  class  of  bodies  known  as  duct- 
less glands,  but  they  are  entirely  different  in  structure  from  the  spleen 
and  lymphatic  glands.  A  section  through  the  fresh  organ  (fig.  222) 


FIG.  222. — A  VERTICAL  SECTION  OF  THE  SUPRARENAL  BODY  OF  A  FCETUS,  TWICE 

THE  NATURAL  SIZE,    SHOWING   THE  DISTINCTION  BETWEEN  THE  MEDULLARY 
AND  CORTICAL  SUBSTANCE.       (A.  Thomson.) 

v,  issuing  vein ;  r,  summit  of  kidney. 

shows  a  cortical  zone  which  is  striated  vertically  to  the  surface,  and  of  a 
yellowish  colour,  and  a  medulla  which  is  soft  and  highly  vascular,  and 
of  a  brownish-red  colour.  The  whole  organ  is  invested  by  a  fibrous 
capsule  which  sends  fibrous  septa  inwards  to  the  cortical  substance  (fig. 
223),  subdividing  this  for  the  most  part  into  columnar  groups  of  cells. 


190 


THE  ESSENTIALS  OF  HISTOLOGY. 


(zona  fasciculata,  c).  Immediately  underneath  the  capsule,  however, 
the  groups  are  more  rounded  (zona  glomerulosa,  /;),  whilst  next  to  the 
medulla  they  have  a  closely  reticular  arrangement  (zona  reticularis,  d), 
and  a  similar  disposition  both  of  the  cells  and  the  connective  tissue  is 
noticeable  throughout  the  medulla. 

The  cells  which  form  the  rounded  groups  and  columns  of  the  cortical 
substance  are  polyhedral  in  form  (fig.  224,  A);  each  contains  a  clear  round 
nucleus,  and  there  are  often  yellowish  oil-globules  in  their  protoplasm. 


FIG.  224,  A. — CELLS  AND  CELL-GROUPS  FROM 

/    j  THE  OUTERMOST  LAYER  OF  THE   CORTICAL 

SUBSTANCE    OF    THE    SUPRARENAL    BODY. 

FIG.  223.— VERTICAL  SECTION  OF  SUPRA-  (Eberth. )  B.— A  SMALL  PORTION  OF  THE 
RENAL  BODY.  (Magnified.)  (Eberth.)  MEDULLARY  PART  OF  THE  SUPRARENAL 

1,  cortical  substance;  2,  medullary  sub-  CAPSULE  OF  THE  OX.  (Eberth.) 

stance  :  a,  capsule  ;  6,  zona  glomerulosa  : 

c,  zona  fasciculata  ;  d,  zona  reticularis  ;  e , 

groups  of  medullary  cells  ;  /,  section  of  a 

large  vein. 

No  blood-vessels  penetrate  between  these  cells,  both  the  blood-vessels 
-and  lymphatics  of  the  cortex  running  in  the  fibrous  septa  between  the 
columns  ;  the  lymphatics  are  said  to  communicate  with  fine  spaces 
which  run  between  the  cells  of  the  columns. 

The  cells  of  the  medulla  (fig.  224,  B)  are  more  irregular  in  shape,  and 
are  often  branched.    Their  protoplasm  is  either  clear,  or  it  may  in  some 


STRUCTURE  OF  THE  THYROID  BODY. 


191 


animals  contain  a  brownish  pigment,  but  in  man  the  dark  red  colour  of 
the  medulla  is  largely  due  to  the  blood  contained  in  the  large  venous 
spaces  by  which  it  is  pervaded,  and  which  receive  the  blood  after  it  has 
traversed  the  capillaries  of  the  cortex.  Investing  the  larger  veins  are 
longitudinal  bundles  of  plain  muscular  fibres  ;  and  numerous  nerves, 
after  traversing  the  cortical  substance,  are  distributed  throughout  the 
medulla,  where  they  form  a  close  plexus  provided  with  ganglion-cells. 
The  cells  of  the  medulla  are  characterised  by  staining  brown  by  chromic 
acid  and  its  salts,  provided  the  organ  is  quite  fresh. 

THE  THYROID  BODY. 

The  thyroid  body  consists  of  a  framework  of  connective  tissue  in- 
closing numerous  spherical  or  oval  vesicles  (fig.  225)  which  are  lined 
with  cubical  epithelium.  The  cavities  of  the  vesicles  are  filled  with  a 
peculiar  viscid  liquid  which  is  coagulated  by  alcohol  and  which  then 
becomes  stained  with  hrernatoxylin.  A  similar  material  has  been  found 


FIG.  225.— SECTION  OF  THE  THYROID  GLAND  OF  A  CHILD. 

Two  complete  vesicles  and  portions  of  others  are  represented.  The  vesicles  are  filled  with 
colloid,  which  also  occupies  the  interstitial  spaces.  In  the  middle  of  one  of  the  spaces  a 
blood-vessel  is  seen  cut  obliquely,  and  close  to  it  is  a  plasma-cell.  Between  the  cubical 
epithelium-cells  smaller  cells  like  lymph-corpuscles  are  here  and  there  seen. 

in  the  lymphatics  of  the  gland,  and  may  sometimes  be  detected  also  in 
the  interstices  of  the  connective  tissue,  as  shown  in  the  figure. 

The  blood-vessels  of  the  thyroid  are  exceedingly  numerous,  and  the 
capillaries  form  close  plexuses  round  the  vesicles.  Some  of  the  blood- 
vessels are  distributed  to  a  peculiar  highly  vascular  embryonic  tissue 
which  occurs  in  patches  here  and  there  in  the  organ  (Horsley). 

Disease  of  the  thyroid  or  its  extirpation  is  accompanied  by  remark- 
able changes  in  the  chemical  composition  of  the  blood  and  many  of  the 
tissues,  resulting  chiefly  in  the  accumulation  within  them  of  a  large 
amount  of  mucin ;  a  condition  of  general  myxcedema,  and  eventually  of 
cretinism,  being  produced. 


192  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  XXXV. 


STRUCTURE  OF  THE  KIDNEY. 

1.  SECTIONS  passing  through  the  whole  kidney  of  a  small  mammal,  such  as  a 
mouse  or  rat.  These  sections  will  show  the  general  arrangement  of  the  organ 
and  the  disposition  of  the  tubules  and  of  the  Malpighian  corpuscles. 

A  general  sketch  should  be  made  of  one  of  these  sections  under  a  low 
power. 

2.  Thin  sections  of  the  kidney  of  a  larger  mammal,  such  as  the  dog,  may 
next  be  studied.     In  some  the  direction  of  the  section  should  be  parallel 
with  the  tubules  of  the  medulla,  and  in  others  across  the  direction  of  those 
tubules.     The  characters  of  the  epithelium  of  the  several  parts  of  the  urini- 
ferous  tubules  are  to  be  made  out  in  these  sections. 

3.  Separate  portions  of  the  uriniferous  tubules  may  be  studied  in  teased 
preparations   from   a   kidney   which   has   been   subjected   to   some   process 
which  renders  it  possible  to  unravel  the  uriniferous  tubules  for  a  certain 
distance.1 

4.  Sections  of  a  kidney  in  which  the  blood-vessels  have  been  injected. 
Examine  these  with  a  low  power  of  the  microscope.     Try  and  follow  the 
course  of  the  arteries — those  to  the  cortex  sending  their  branches  to  the 
glomeruli,  those  to  the  medulla  rapidly  dividing  into  pencils  of  fine  vessels 
which  run  between  the  straight  uriniferous  tubules  of  that  part.     Notice  also 
the  efferent  vessels  from  the  glomeruli  breaking  up  into  the  capillaries  which 
are  distributed  to  the  tubules  of  the  cortical  substance. 

Make  sketches  showing  these  points. 


The  kidney  is  a  compound  tubular  gland.  To  the  naked  eye  it 
appears  formed  of  two  portions — a  cortical  and  a  medullary.  The  latter 
is  subdivided  into  a  number  of  pyramidal  portions  (pyramids  of 
Malpighi),  the  base  of  each  being  surrounded  by  cortical  substance, 
while  the  apex  projects  in  the  form  of  a  papilla  into  the  dilated  com- 
mencement of  the  ureter  (pelvis  of  the  kidney).'2  Both  cortex  and 
medulla  are  composed  entirely  of  tubules— the  uriniferous  tubules — 
which  have  a  straight  direction  in  the  medulla  and  a  contorted  arrange- 
ment in  the  cortex ;  but  groups  of  straight  tubules  also  pass  from  the 
medulla  through  the  thickness  of  the  cortex  (medullary  rays,  see  fig.  226). 

1  For  a  method  which  may  be  employed  for  this  purpose,  see  Course  of  Practi- 
cal Histology. 

2  In  many  animals  the  whole  kidney  is  formed  of  only  a  single  pyramid,  but  in 
man  there  are  about  twelve. 


STRUCTURE  OF  THE  KIDNEY. 


193 


The  uriniferous  tubules  begin  in  the  cortical  part  of  the  organ  in 
dilatations,  each  inclosing  a  tuft  or  glomerulus  of  convoluted  capillary 
blood-vessels  (corpuscles  of  Malpighi),  the  dilated  commencement  of 


FlG.  226. — DlAGEAM  OF  THE  CURVE  OF  THE  TUBULES  IN  A  UNIPYBAMIDAL  KIDNEY, 
SUCH  AS  THAT  OF  THE  RABBIT.      (Toldt.) 

a,  Malpighian  bodies  ;  6,  first  convoluted  tubule  ;  c,  d,  looped  tube  of  Henle  ;  e,  second 
convoluted  ;  /,  collecting  tube  ;  g,  ducts  of  Bellini. 

the  tubule  being  known  as  the  capsule  (fig.  227,  1).  The  tubule  leaves 
the  capsule  by  a  neck  (2),  which  is  sometimes  narrowed,  and  in  some 
animals  (e.g.  frog)  is  long,  and  has  ciliated  epithelium  ;  the  tubule  is  at 
first  convoluted  (first  convoluted  tubule,  3),  but  soon  becomes  nearly 
straight  or  slightly  spiral  only  (spiral  tubule,  4),  and  then,  rapidly 
narrowing,  passes  down  into  the  medulla  towards  the  dilated  com- 
mencement of  the  ureter  as  the  descending  tubule  of  Henle  (5).  It  does 
not  at  once,  however,  open  into  the  pelvis  of  the  kidney,  but  before 
reaching  the  end  of  the  papilla  it  turns  round  in  the  form  of  a  loop 
(loop  of  Henle,  6)  and  passes  upwards  again  towards  the  cortex,  parallel 
to  its  former  course  and  at  first  somewhat  larger  than  before,  but 
afterwards  diminishing  in  size  (ascending  tubule  of  Henle,  7,  8,  9).  Arrived 
at  the  cortex,  it  approaches  close  to  the  capsule  from  which  the  tubule 
took  origin,  but  at  a  point  opposite  to  the  origin,  viz.  near  the  afferent  and 
efferent  vessels  of  the  glomerulus  (Golgi).  It  then  becomes  larger  and 
irregularly  zigzag  (zigzag  tubule,  10),  and  may  again  be  somewhat  con- 
voluted (second  convoluted  tubule,  11),  eventually,  however,  narrowing  into 

N 


194 


THE  ESSENTIALS  OF  HISTOLOGY. 


a  vessel  (junctional  tubule,  12)  which  joins  a  straight  or  collecting  tubule 
(13).  This  now  passes  straight  through  the  medullary  substance  of  the 
kidney  (14)  to  open  at  the  apex  of  the  papilla  as  one  of  the  ducts  of 
Bellini  (15). 


FIG.  227.— DIAGRAM  OF  THE  COURSE  OF  TWO  URINIFEROUS  TUBULES.    (Klein.) 

A,  cortex ;  B,  boundary  zone ;  c,  papillary  zone  of  the  medulla ;  a,  a',  superficial  and  deep 
layers  of  cortex,  free  from  glomeruli.    For  the  explanation  of  the  numerals,  see  the  text. 

The  tubules  are  throughout  bounded  by  a  basement-membrane,  which 
is  lined  by  epithelium,  but  the  characters  of  the  epithelium-cells  vary 


STKUCTUEE  OF  THE  KIDNEY. 


19f) 


in  the  different  parts  of  a  tubule.  In  the  capsule  the  epithelium  is 
flattened  and  is  reflected  over  the  glomerulus  (fig.  228,  a).  In  the  first 
convoluted  and  spiral  tubules  it  is  thick,  and  the  cells  show  a  marked 


FIG.  228.— TUBULES  FROM  A  SECTION  OP  THE  DOG'S  KIDNEY.     (Klein.) 

«,  capsule,  inclosing  the  glomerulus;  n,  neck  of  the  capsule;  c,  c,  convoluted  tubules;  b, 
irregular  tubules ;  d,  collecting  tube  ;  e,  e,  spiral  tubes  ;  /,  part  of  the  ascending  limb  of 
Henle's  loop,  here  (in  the  medullary  ray)  narrow. 

fibrillar  structure  (figs.  229,  230).     Moreover,  they  interlock  laterally 
and  are  difficult  of  isolation ;  in  some  animals  they  have  been  described 


FIG.  229. — STRUCTURE  OP  THE  EPITHELIUM  OP  THE  CONVOLUTED  TUBULES. 
(Heidenhain.) 

<l,  section  of  a  convoluted  tubule  from  the  rat,  showing  the  unaltered  protoplasm  occupying 
a  circular  area  around  the  nucleus  of  each  cell ;  a,  6,  c,  isolated  cells  from  the  convoluted 
tubules  of  the  rat ;  e,  isolated  cells  from  the  dog's  kidney,  viewed  from  the  inner  surface, 
and  showing  the  irregular  contour  of  the  protoplasm  ;  /,  isolated  cells  from  the  newt, 
showing  the  rods  and  a  homogeneous  cuticular  layer. 


196 


THE  ESSENTIALS  OF  HISTOLOGY. 


as  being  ciliated.  They  certainly  often  exhibit  a  brush  of  cilium- 
like  processes  projecting  into  the  lumen,  but  it  is  doubtful  if  these 
are  vibratile.  In  the  narrow  descending  limb  of  the  looped  tubule 
(fig.  231,  c),  and  in  the  loop  itself,  the  cells  are  clear  and  flattened 
and  leave  a  considerable  lumen ;  in  the  ascending  limb  they  again 
acquire  the  striated  structure  and  nearly  fill  the  lumen.  The 


FIG.  230.— PART  OF  A  CON- 
VOLUTED TUBULE  FROM  THE  DOG'S 
KIDNEY.  (Heidenhain). 


FIG.  231. — PORTIONS  OF  TUBULES,  ISOLATED. 
(Cadiat.) 

a,  large  collecting  tubule  ;  b,  loop  of  Henle ;  c,  descend- 
ing tubule  of  Henle. 

fibrillations  of  the  cells  are  still  more  marked  in  the  zigzag  tubules 
(fig.  228,  b),  and  a  similar  structure  is  present  also  in  the  second 
convoluted  tubules,  into  which  these  pass.  On  the  other  hand,  the 
functional  tubule  has  a  large  lumen  and  is  lined  by  clear  flattened 
cells,  and  the  collecting  tabes  have  also  a  very  distinct  lumen  and 
are  lined  by  a  clear  cubical  or  columnar  epithelium  (figs.  228,  d  : 
231,  a). 


STEUCTUEE  OF  THE  KIDNEY. 


197 


The  following  gives  a  tabular  view  of  the  parts  which  compose 
a  uriniferous  tubule,  and  the  nature  of  the  epithelium  in  each 
part : — 


Portion  of  tubule. 

Nature  of  epithelium. 

Position  of  tubule. 

Capsule 

Flattened,  reflected  over  glomerulus  . 

Labyrinth  of  cortex.1 

First   convoluted 

Cubical,    fibrillated,    the   cells   inter- 

Labyrinth of  cortex. 

tube 

locking 

Spiral  tube. 

Cubical,  fibrillated  (like  the  last) 

Medullary  ray  of  cor- 

tex. 

Small  or  descend- 

Clear flattened  cells    .... 

Boundary   zone   and 

ing      tube      of 

partly       papillary 

Henle 

zone  of  medulla. 

Loop  of  Henle     . 

Like  the  last       ..... 

Papillary     zone      of 

medulla. 

Larger  or  ascend- 

Cubical, fibrillated,  sometimes  imbri- 

Medulla, and  medul- 

ing     tube      of 

cated 

lary  ray  of  cortex. 

Henle 

Zigzag  tube 

Cells  strongly  fibrillated  ;  varying  in 

Labyrinth  of  cortex. 

height  ;  lumen  small 

Second        convo- 

Similar to  first  convoluted  tube,  but 

Labyrinth  of  cortex. 

luted  tube 

cells  are  longer,  with  larger  nuclei, 

and  they  have  a  more  refractive 

aspect 

Junctional  tube  . 

Clear  flattened  and  cubical  cells 

Labyrinth  passing  to 

medullary  ray. 

Straight   or    col- 

Clear cubical  and  columnar  cells 

Medullary   ray    and 

lecting  tube 

medulla. 

Duct  of  Bellini    . 

Clear  columnar  cells   .... 

Opens    at    apex     of 

papilla. 

Blood-vessels. — The  renal  artery  divides  into  branches  on  entering 
the  organ,  and  these  branches  pass  towards  the  cortex,  forming  in- 
complete arches  between  the  cortex  and  the  medulla  (fig.  233,  a). 
The  branches  of  the  renal  vein  form  similar  but  more  complete 
arches  (g).  From  the  arterial  arches  vessels  pass  through  the  cortex 
(interlobular  arteries,  &),  and  give  off  at  intervals  small  arterioles 
(efferent  vessels  of  the  glomeruli),  each  of  which  enters  the  dilated 
commencement  of  a  uriniferous  tubule,  within  which  it  forms  a 
glomerulus.  From  the  glomerulus  a  somewhat  smaller  efferent  vessel 
passes  out,  and  this  at  once  again  breaks  up  into  capillaries,  which 
are  distributed  amongst  the  tubules  of  the  cortex  (e) ;  their  blood  is 
collected  by  veins  which  accompany  the  arteries  and  join  the  venous 
arches  between  the  cortex  and  the  medulla,  receiving  in  their  course 
certain  other  veins  which  arise  by  radicles  having  a  somewhat  stellate 
arrangement  near  the  capsule  (vence  stellulce,  j). 

The  medulla  derives  its  blood-supply  from   special  offsets   of  the 


1  The  part  of  the  cortex  between  and  surrounding  the  medullary  rays  is  so  named. 


198 


THE  ESSENTIALS  OF  HISTOLOGY. 


arterial  arches,  which  almost  immediately  break  up  into  pencils  of  fine 
straight  arterioles  running  in  groups  between  the  straight  tubules  of 
the  medulla.  These  arterioles  gradually  break  up  into  a  capillary  net- 


FIG.  232. — SECTION  ACROSS  A  PAPILLA  OF  THE  KIDNEY.    (Cadiat.) 
a,  large  collecting  tubes  (ducts  of  Bellini) ;  b,  c,  d,  tubules  of  Heiile  ;  e,  f,  blood-capilLaries. 

work  with  elongated  meshes  which  pervades  the  medulla  (fig.  233,  /), 
and  which  terminates  in  a  plexus  of  somewhat  larger  venous  capillaries 
in  the  papillae.  From  these  and  from  the  other  capillaries  the  veins 
collect  the  blood,  and  pass,  accompanying  the  straight  arterioles,  into 
the  venous  arches  between  the  cortex  and  medulla.  The  groups  of 
small  arteries  and  veins  (wsa  recta)  in  the  part  of  the  medulla  nearest 
the  cortex  alternate  with  groups  of  the  uriniferous  tubules,  and  this 
arrangement  confers  a  striated  aspect  upon  this  portion  of  the  medulla 
(boundary  zone,  see  fig.  234,  g). 

The  efferent  vessels  of  those  glomeruli  which  are  situated  nearest 
to  the  medulla  may  also  break  up  into  pencils  of  fine  vessels  (false 
arterm  rectce)  and  join  the  capillary  network  of  the  medulla  (fig.  233,  d). 

Between  the  uriniferous  tubules,  and  supporting  the  blood-vessels^ 
is  a  certain  amount  of  connective  tissue  (fig.  232),  within  which  are 
cleft-like  spaces  from  which  the  lymphatics  of  the  organ  originate. 


STRUCTURE  OF  THE  KIDNEY. 


199 


FIG.  234. — SECTION  THROUGH  PART 

OP  THE  DOG'S  KIDNEY.    (Ludwig.) 

p,  papillary,  and  g,  boundary  zones  of 
the  medulla;  c,  cortical  layer;  h, 
bundles  of  tubules  in  the  boundary 
layer,  separated  by  spaces,  6,  con- 
taining bunches  of  vessels  (not  here 
represented),  and  prolonged  into  the 
cortex  as  the  medullary  rays,  m  ;  c, 
intervals  of  cortex,  composed  chiefly 
of  convoluted  tubules,  with  irregu- 
lar rows  of  glomeruli,  between  the 
medullary  rays. 


FIG.  233. —VASCULAR  SUPPLY  OF  KIDNEY. 
(Cadiat.) 

a,  part  of  arterial  arch ;  &,  interlobular  artery ; 
c,  glomerulus  ;  d,  efferent  vessel  passing  to 
medulla  as  false  arteria  recta ;  e,  capillaries  of 
cortex ;  /,  capillaries  of  medulla ;  g,  venous 
arch ;  h,  straight  veins  of  medulla ;  j,  vena 
stellula ;  i,  interlobular  vein. 


200  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  XXXVI. 

STRUCTURE  OF  THE  URETER,  BLADDER,  AND  MALE 
GENERATIVE  ORGANS. 

1.  SECTION  across  the  ureter. 

2.  Section  of  the  urinary  bladder  vertical  to  the  surface. 

In  the  sections  of  the  ureter  and  of  the  urinary  bladder,  notice  the  tran- 
sitional epithelium  resting  on  a  mucous  membrane,  which  is  composed  chiefly 
of  areolar  tissue  without  glands,  and  the  muscular  coat  outside  this.  In  the 
ureter  there  is  some  fibrous  tissue  outside  the  muscular  coat,  and  at  the  upper 
part  of  the  bladder  there  is  a  layer  of  serous  membrane  covering  the  muscular 
tissue.  Sketch  a  section  of  the  ureter  under  a  low  power,  and  the  epithelium 
of  the  bladder  under  the  high  power. 

3.  Section  across  the  penis.     The  blood-vessels  of  the  organ  should  have 
been  injected  with  the  hardening  fluid  so  as  the  better  to  exhibit  the  arrange- 
ment of  the  venous  spaces  which  constitute  the  erectile  tissue.     Notice  the 
large  venous  sinuses  of  the  corpora  cavernosa  and  the  smaller  spaces  of  the 
corpus  spongiosum,  in  the  middle  of  which  is  seen  the  tube  of  the  urethra. 

4.  Section  across  the  testis  and  epididymis.     The  sections  are  best  made 
from  a  rat's  testis  which  has  been  hardened  in  alcohol,  and  thin  pieces  of 
which  have  been  stained  in  bulk  in  hsematoxylin.     In  these  sections  notice 
the  strong  capsule  surrounding  the  gland,  the  substance  of  which  consists  of 
tubules  which  are  variously  cut,  and  the  epithelium  in  which  is  in  different 
conditions  of  development  in  the  different  tubules.     Observe  the  strands  of 
polyhedral  interstitial  cells  lying  in  the  loose  tissue  between  the  tubules  and 
the  lymphatic  clefts  in  that  tissue.     Notice  also  in  sections  through  the 
epididymis  the  ciliated  epithelium  of  that  tube. 

Sketch  carefully  under  a  high  power  the  contents  of  some  of  the  semini- 
ferous tubules  so  as  to  illustrate  the  mode  of  formation  of  the  spermatozoa. 

5.  Examination  of  spermatozoa.     The  spermatozoa  may  be  obtained  fresh 
from  the  testis  or  seminal  vesicles  of  a  recently  killed  animal  and  examined 
in  saline  solution.     Their  movements  may  be  studied  on  the  warm  stage  ;  to 
display  their  structure  a  very  high  power  of  the  microscope  is  necessary. 
Measure  and  sketch  three  or  four  spermatozoa. 


The  ureter  is  a  muscular  tube  lined  by  mucous  membrane.  The 
muscular  coat  consists  of  two  layers  of  plain  muscular  tissue,  an  outer 
circular,  and  an  inner  longitudinal.  In  the  lower  part  there  are  some 
longitudinal  bundles  external  to  the  circular.  Outside  the  muscular 
coat  is  a  layer  of  fibrous  tissue  in  which  the  blood-vessels  and  nerves 
ramify  before  entering  the  muscular  layer. 


STRUCTURE  OF  THE  URETER 


201 


The  mucous  membrane  is  composed  of  areolar  tissue  and  is  lined  by 
transitional  epithelium. 

The  urinary  bladder  has  a  muscular  wall  lined  by  a  strong  mucous 
membrane  and  covered  in  part  by  a  serous  coat. 

The  muscular  coat  consists  of  three  layers,  but  the  innermost  is 
incomplete.  The  principal  fibres  run  longitudinally  and  circularly, 
and  the  circular  fibres  are  collected  into  a  layer  of  some  thickness 
which  immediately  surrounds  the  commencement  of  the  urethra,  form- 
ing the  sphincter  vesicce.  The  mucous  membrane  is  lined  by  a  transitional 
stratified  epithelium  like  that  of  the  ureter.  The  shape  and  structure 
of  the  cells  have  already  been  studied  (Lesson  VII.). 

The  nerves  to  the  bladder  form  gangliated  plexuses,  and  are  dis- 
tributed mainly  to  the  muscular  tissue  and  blood-vessels,  but  some  are 
said  to  enter  the  epithelium. 


FIG.  235. — SECTION  OP  ERECTILE  TISSUE.     (Cadiat.) 

a,  trabeculse  of  connective  tissue,  with  elastic  fibres,  and  bundles  of  plain  muscular 
tissue  (c) ;  6,  venous  spaces. 

The  penis  is  mainly  composed  of  cavernous  tissue  which  is  collected 
into  two  principal  tracts — the  corpora  cavernosa,  one  on  each  side,  and 
the  corpus  spongiosum  in  the  middle  line  inferiorly.  All  these  are 
bounded  by  a  strong  capsule  of  fibrous  and  plain  muscular  tissue, 
containing  also  many  elastic  fibres  and  sending  in  strong  septa  or 
trabeculse  of  the  same  tissues,  w^hich  form  the  boundaries  of  the  caver- 
nous spaces  of  the  erectile  tissue  (fig.  235).  The  arteries  of  the  tissue 
run  in  these  trabeculse,  and  their  capillaries  open  into  the  cavernous 
spaces.  On  the  other  hand,  the  spaces  are  connected  with  efferent 


202 


THE  ESSENTIALS  OF  HISTOLOGY. 


veins.  The  arteries  of  the  cavernous  tissue  may  sometimes  in  injected 
specimens  be  observed  to  form  looped  or  twisted  projections  into  the 
cavernous  spaces  (helicine  arteries  of  Mutter). 

Urethra. — The  cross-section  of  the  urethra  appears  in  the  middle  of 
the  corpus  spongiosum  in  the  form  of  a  transverse  slit.  It  is  lined  in 
the  prostatic  part  by  transitional,  but  elsewhere  by  columnar  epi- 
thelium, except  near  its  orifice,  where  the  epithelium  is  stratified  scaly. 
In  the  female  urethra  it  is  scaly  throughout.  The  epithelium  rests 
upon  a  vascular  mucous  membrane,  and  this  again  is  supported  by  a 
coating  of  submucous  tissue,  containing  two  layers  of  plain  muscular- 
fibres — an  inner  longitudinal  and  an  outer  circular.  Outside  this  again 
is  a  close  plexus  of  small  veins  which  are  connected  with,  and  may  be 
said  to  form  part  of,  the  corpus  spongiosum. 

The  mucous  membrane  of  the  urethra  is  beset  with  small  mucous 
glands,  simple  and  compound  (glands  of  Littre).  There  are  also  a 

number  of  oblique  recesses  termed  lacunw. 
Besides  these  small  glands  and  glandular 
recesses,  two  compound  racemose  glands 
open  into  the  bulbous  portion  of  the  urethra 
(Cowper's  glands).  Their  acini  are  lined  by  clear 
columnar  cells  which  yield  a  mucous  secretion. 
The  prostate,  which  surrounds  the  com- 
mencement of  the  urethra,  is  a  muscular  and 
glandular  mass,  the  glands  of  which  are 
composed  of  tubular  alveoli,  lined  by  colum- 
nar epithelium,  with  smaller  cells  lying  be- 
tween them  and  the  basement-membrane. 
Their  ducts  open  upon  the  floor  of  the 
urethra. 

The  integument  of  the  penis  contains 
numerous  special  nerve  end-organs  of  the 
nature  of  end-bulbs,  and  Pacinian  bodies 
are  also  found  upon  the  nerves.  Lym- 
phatic vessels  are  numerous  in  the  in- 
tegument of  the  organ  and  also  in  the  sub- 
mucous  tissue  of  the  urethra. 

The  testicle  is  inclosed  by  a  strong  fibrous 
capsule,  the  tunica  albuginea  (fig.  236,  i). 
This  is  covered  externally  with  a  layer  of  serous  epithelium  reflected 
from  the  tunica  vaginalis.  From  its  inner  surface  there  proceed  fibrous 
processes  or  trabeculce,  which  imperfectly  subdivide  the  organ  into 
lobules,  and  posteriorly  the  capsule  is  prolonged  into  the  interior  of  the 


FIG.  236.— PLAN  OF  A  VER- 
TICAL SECTION  OF  THE  TES- 
TICLE, SHOWING  THE  AR- 
RANGEMENT OF  THE  DUCTS. 

The  true  length  and  diameter  of 
the  ducts  have  been  disregard- 
ed, a,  a,  tubuli  seminiferi 
coiled  up  in  the  separate  lobes; 
b,  vasa  recta  ;  c,  rete  vascu- 
losum  ;  d,  vasa  efferentia  end- 
ing in  the  coni  vasculosi;  l,e,g, 
convoluted  canal  of  the  epi- 
didymis  ;  h,  vas  deferens  ;  /, 
section  of  the  back  part  of  the 
tunica  albuginea ;  i,  i,  fibrous 
processes  running  between  the 
lobes  ;  /  to  s,  mediastinum. 


MALE  GENEEATIVE  OEGANS. 


203 


gland  in  the  form  of  a  mass  of  fibrous  tissue,  which  is  known  as  the 
mediastinum  (fig.  236,  /).  Attached  to  the  posterior  margin  of  the  body 
of  the  gland  is  a  mass  (epididymis,  e)  which  when  investigated  is  found 
to  consist  of  a  single  convoluted  tube,  receiving  at  its  upper  end  the 
efferent  ducts  of  the  testis  and  prolonged  at  its  lower  end  into  a  thick- 
walled  muscular  tube,  the  vas  deferens,  which  conducts  the  secretion  to 
the  urethra. 

The  glandular  substance  of  the  testicle  is  wholly  made  up  of  con- 
voluted tubules,  which  when  unravelled  are  of  very  considerable  length. 


FIG.  237.— PASSAGE  OF  CONVOLUTED  SEMINIFEROUS  TUBULES  INTO  STRAIGHT  TUBULES 

AND  OF  THESE  INTO  THE  RETE  TESTIS.      (Mihalkowics. ) 

a,  seminiferous  tubules  ;  b,  fibrous  stroma  continued  from  the  mediastinum  testis  ;  c,  rete  testis. 

Each  commences  near  the  tunica  albuginea,  and  after  many  windings 
terminates,  usually  after  joining  one  or  two  others,  in  a  straight  tubvle 
(fig.  236,  b),  which  passes  into  the  mediastinum,  and  there  forms,  by 
uniting  with  the  other  straight  tubules,  a  network  of  intercom- 
municating vessels,  which  is  known  as  the  rete  testis.  From  the  rete  a 
certain  number  of  efferent  tubules  arise,  and  after  a  few  convolutions 
pass  into  the  tube  of  the  epididymis. 


204 


THE  ESSENTIALS  OF  HISTOLOGY. 


Structure  of  the  tubules. — The  seminiferous  tubules  are  formed  of  a 
thick  basement-membrane,  and  contain  several  layers  of  epithelium- 
cells.  Of  these  layers,  the  one  next  the  basement-membrane  is  a 
stratum  of  clear  cubical  cells  (lining  epithelium,  fig.  241,  a),  the  nuclei 
of  which,  for  the  most  part,  exhibit  the  irregular  network  which  is 
characteristic  of  the  resting  condition,  but  in  certain  tubules  they 
exhibit  indications  of  division.  Here  and  there  these  epithelium-cells 
appear  enlarged,  and  project  between  the  more  internal  layers,  being 
connected  with  groups  of  developing  spermatozoa.  These  enlarged 
cells  may  be  termed  sustentacular  cells  (fig,  241,  a').1 


FIG.  238.— SECTION  OF  PARTS  OF  THREE  SEMINIFEROUS  TUBULES  OF  THE  RAT. 

a,  with  the  spermatozoa  least  advanced  in  development ;  6,  more  advanced  ;  c,  containing 
fully  developed  spermatozoa.  Between  the  tubules  are  seen  strands  of  interstitial-cells 
with  blood-vessels  and  lymph-spaces. 

Next  to  this  epithelium  is  seen  a  zone  of  larger  cells  (spermatogenic 
cells,  fig.  241,  6),  the  nuclei  of  which  have  the  skein-like  aspect  which  is 
typical  of  commencing  division ;  these  cells  may  be  two,  three,  or  more 
deep  (as  in  a,  fig.  238).  Next  to  them,  and  most  internal,  is  to  be  seen 
in  some  tubules  (b  and  c)  a  large  number  of  small  protoplasmic  cells 
with  simple  circular  nuclei  (spermatoblasts,  fig.  241,  c).  In  other  tubules 
these  cells  are  elongated,  and  the  nucleus  is  at  one  end,  and  in  others 
again  these  elongated  cells  are  converted  into  evident  spermatozoa, 
which  lie  in  groups  with  their  heads  projecting  between  the  deeper 
cells  and  connected  with  one  of  the  enlarged  cells  of  the  lining  epi- 

1  These  are  the  '  spermatoblasts '  of  some  authors — a  name  given  to  them  on 
the  erroneous  supposition  that  they  directly  produce  the  spermatozoa.  The  term 
'  spermatoblast '  is  more  applicable  to  the  small  cells  of  the  third  layer  or  zone, 
and  will  be  so  applied  here. 


STRUCTURE  OF  THE  TESTICLE. 


205 


thelium,  and  their  tails  emerging  into  the  lumen  of  the  tubule  (fig. 
238,  b).  As  they  become  matured  they  gradually  pass  altogether 
towards  the  lumen,  where  they  eventually  become  free  (c).  During 
the  time  that  this  crop  of  spermatozoa  has  been  forming,  another  set 
of  spermatoblasts  has  been  produced  by  the  division  of  the  spermato- 
genic  cells,  and  on  the  discharge  of  the  spermatozoa  the  process  is 
repeated  as  before. 

The  straight  tubules  which  lead  from  the  convoluted  seminiferous 
tubes  into  the  rete  testis  (fig.  237)  are  lined  only  by  a  single  layer  of 
clear  flattened  or  cubical  epithelium.  The  tubules  of  the  rete  also  have 
a  simple  epithelial  lining,  but  the  basement-membrane  is  here  absent, 
the  epithelium  being  supported  directly  by  the  connective  tissue  of  the 
mediastinum. 


FIG.  239.— SECTION  ACROSS  THE  COMMENCEMENT  OF  THE  VA* 
DEFERENS.     (Klein. ) 

a,  epithelium  ;  6,  mucous  membrane  ;  c,  d,  e,  inner,  middle,  and  outer  layers  of  the  muscular 
coat ;  /,  bundles  of  the  internal  cremaster  muscles  ;  g,  section  of  a  blood-vessel. 

The  efferent  tubules  which  pass  from  the  rete  to  the  epididymis, 
and  the  tube  of  the  epididymis  itself,  are  lined  by  columnar  ciliated 
epithelium,  the  cilia  being  very  long ;  these  tubes  have  a  considerable 
amount  of  plain  muscular  tissue  in  their  wall. 

The  vas  deferens  (fig.  239)  is  a  thick  tube,  the  wall  of  which  is 
formed  of  an  outer  thick  layer  of  longitudinal  bundles  of  plain  muscular 


206 


THE  ESSENTIALS  OF  HISTOLOGY. 


tissue ;  within  this  an  equally  thick  layer  of  circular  bundles  of  the  same 
tissue,  and  within  this  again  a  thin  layer  of  longitudinal  muscle.  The 
tube  is  lined  by  a  mucous  membrane,  the  inner  surface  of  which  is 
covered  by  columnar  non-ciliated  epithelium. 

The  ampullce  of  the  vasa  deferentia,  and  the  vesiculce  seminales,  are 
in  structure  similar  to  the  vas  deferens,  but  their  corrugated  walls 
are  much  thinner. 

The  connective  tissue  between  the  tubules  of  the  testis  is  of  very 
loose  texture,  and  contains  numerous  lymphatic  clefts,  which  form  an 
intercommunicating  system  of  commencing  lymphatic  vessels.  Lying 
in  this  intertubular  tissue  are  strands  of  polyhedral  epithelium-like 
cells  (interstitial  cells,  see  fig.  238)  of  a  yellowish  colour;  they  are 
much  more  abundant  in  some  species  of  animals  (cat,  boar)  than  in 
others.  They  accompany  the  blood-vessels  before  these  break  up  to 
form  the  capillary  networks  which  cover  the  walls  of  the  seminiferous 
tubules. 

The  spermatozoa. — Each   spermatozoon  consists  of  three  parts,  a 
Jiead,  a  middle  part  or  body,  and  a  long  tapering  and  vibratile  tail. 
In  man  (fig.  240)  the  head  is  of  a  flattened  oval  shape, 
somewhat  more  flattened  and  pointed  anteriorly ;  it  is 
said  to  be  provided  with  a  small  barb-like  projection 
at  its  extremity  (Dowdeswell).     The  middle-piece  is 
short  and  cylindrical,  and  appears  to  have  a  spiral 
fibre  passing  round  it.     The  tail  is  the  longest  part  of 
the  spermatozoon,    and   during   life   is  in  continual 
vibratile   motion,  the  action  resembling  that  of  the 
cilia  of  a  ciliated  epithelium-cell.     The  extremity  of 
the    tail    (end-piece)   forms   a   distinct    part    of    the 
spermatozoon,    and   in   some    animals    may   become 
split  up  into  two  or  three  fibrils.     Human  sperma- 
tozoa are  about  ^J^-inch  long.     In  different  animals 
the  shape  of  the  head  and  the  extent  of  the  middle- 
piece  and  tail  vary  greatly.     In  the  rat  (fig.  242,  7) 
the  head  is  long,  and  is  recurved  anteriorly;   it  is 
set  obliquely  on  the  middle -piece,  which  is  also  of 
considerable  extent,  and  has  a  closely  wound  spiral 
filament   encircling   it   in   its   whole   length   (H.   H. 
Brown).     In  the  newt  the  head  is  long  and  tapering, 
and  the  tail  appears  to  have  a  membranous  expansion, 
attached  in  a  spiral  manner  along  its  whole  length.       This  has  also 
been  described  in  the  human  spermatozoon,  but  its  existence  here  is 
doubtful. 


FIG.  240.— HUMAN 
SPERMATOZOA. 
(Retzius.)  i-0/^. 

1, in  profile;  2,viewed 
on  the  flat;  b,  head; 
c,  middle-piece ;  d, 
tail ;  e,  end-piece  of 
the  tail,  which  is  de- 
scribed as  a  distinct 
part  by  Retzius. 


STEUCTURE  OF  THE  SPERMATOZOA.  2)7 

Spermatogenesis. — The  spermatozoa  are  developed  from  the  small  cells 
(spermatoblasts)  which  form  the  innermost  stratum  of  the  seminal  epi- 
thelium, and  these  are  themselves  produced  by  the  division  of  the  large 
spermatogeiiic  or  mother-cells  of  the  second  layer.  It  is  probable  that  these 
mother-cells  again  are  formed  by  division  of  some  of  the  lining  epithelium- 
cells.  The  cycle  of  changes  therefore  which  appears  to  take  place  is  as 
follows  : — 1.  Division  of  a  lining  epithelium-cell  into  two,  one  of  which 
becomes  a  spermatogen,  and  passes  into  the  second  layer,  while  the  other 
remains  in  the  first  layer,  undergoes  enlargement,  and  becomes  a  susten- 
tacular  cell.  2.  Division  of  the  spermatogen.  3.  Further  division  and 
multiplication  of  the  spermatogens  and  the  conversion  of  the  resulting 
daughter-cells  into  a  group  of  spermatoblasts.  4.  Elongation  of  the  sperma- 
toblasts and  their  gradual  conversion  into  mature  spermatozoa.  As  they 


FIG.  241. — DIAGRAM  EXHIBITING  THE  CYCLE  OF  PHASES  OF  SPERMATOGENESIS  (RAT). 

a,  lining  epithelium-cells,  seen  dividing  in  6 ;  a',  sustentacular-cells ;  6,  spermatogenic  or 
mother-cells,  with  skein-like  nuclear  filaments.  These  cells  are  seen  actively  dividing 
in  5.  c,  spermatoblasts,  forming  an  irregular  column  or  clump  in  6,  7,  8,  and  1,  and 
connected  to  an  enlarged  supporting  cell,  a',  of  the  lining  epithelium  in  2,  3,  4,  and  5. 
In  6,  7,  and  8  advanced  spermatozoa  of  one  crop  are  seen  between  columns  of  sperma- 
toblasts of  the  next  crop,  s',  parts  of  the  spermatoblasts  which  are  disintegrated  when 
the  spermatozoa  are  fully  formed ;  s,  seminal  granules  resulting  from  their  disintegra- 
tion ;  a"  in  1  and  2  are  nuclei  of  supporting  cells  which  are  probably  becoming  extruded. 

undergo  this  conversion  their  grouping  becomes  more  evident,  and  each  group 
is  found  to  be  connected  with  a  sustentacular  cell,  which  probably  ministers 
to  their  nutrition.  This  cell  undergoes  a  gradual  process  of  elongation  so 
that  the  spermatozoa  by  the  time  they  are  fully  developed  are  brought  to 
the  lumen  of  the  tube,  in  which  they  then  become  free.  In  the  meantime 
other  alternate  groups  of  daughter-cells  from  which  the  next  crop  of  sperma- 
tozoa will  be  derived  are  being  formed  in  the  same  manner,  passing  through 
the  same  cycle  of  changes.  So  that  in  a  section  of  the  same  tubule,  at  least 


208 


THE  ESSENTIALS  OF  HISTOLOGY. 


two  different  phases  of  development  may  be  observed,  and  in  different 
tubules  of  the  same  testicle  every  phase  may  be  traced.  The  accompanying 
diagram  (fig.  241),  which  is  constructed  from  drawings  by  H.  H.  Brown, 
illustrates  the  cycle  of  changes  above  described  :  it  is  divided  into  eight 
parts,  each  of  which  shows  the  condition  of  the  epithelium  of  a  seminiferous 
tubule  at  a  particular  stage. 

Each  spermatoblast  becomes  converted  into  a  spermatozoon  in  the  follow- 
ing manner  (fig.  242).  The  nucleus  forms  the  head,  while  the  tail  develops 
as  a  fine  filament  within,  but  subsequently  growing  out  from,  the  protoplasm, 
and  apparently  connected  with  the  nucleus  almost  from  the  first.  The 
protoplasm  appears  to  assist  in  forming  the  middle  piece  of  the  spermatozoon  ; 
but  a  considerable  portion  of  the  protoplasm  of  each  daughter-cell  con- 
taming  a  number  of  small  darkly  staining  particles  (seminal  granules)  always 
becomes  detached  and  disintegrated  before  the  spermatozoon  is  fully  mature 
(fig.  241,  ,,  s'). 


i 


FIG.  242. — SPEKMATOBLASTS  FROM  THE  RAT  IN  DIFFERENT  STAGES  OF  DEVELOPMENT. 

(H.  H.  Brown.) 

1-6,  developing  spermatozoa  from  the  testicle  ;  7,  a  mature  spermatozoon  from  the  vas  deferens. 
The  remains  of  the  protoplasm  of  the  cell,  which  is  seen  in  6  still  adhering  to  the  middle 
piece  of  the  spermatozoon  and  containing  a  number  of  dark  granules,  is  thrown  off  as  the 
spermatozoon  matures. 


GENERATIVE  ORGANS  OF  THE  FEMALE. 


209 


LESSON  XXXVII. 

GENERATIVE  ORGANS  OF  THE  FEMALE,  AND  MAMMARY 

GLANDS. 


1.  SECTIONS  of  the  ovary  of  the  rabbit  or  cat.  Study  the  sections  with  a  low 
power,  observing  the  small  and  large  Graafian  vesicles,  each  inclosing  an 
ovum,  scattered  through  the  stroma.  Measure  some  Graafian  vesicles  of 
different  sizes  ;  make  a  general  sketch  of  a  section  under  the  low  power. 
Then  sketch  carefully  two  or  more  of  the  Graafian  vesicles  with  their  con- 
tents. 

2.  Sections  across  the  Fallopian  tube.     Sketch  a  section  under  the  low 
power. 

3.  Section  across  the  body  of  the  uterus.     Observe  with  the  naked  eye 
the  thickness  of  the  muscular  and  mucous  coats  respectively.     Notice  the 
ciliated  columnar  epithelium  lining  the  organ  and  extending  into  the  glands 
of  the  mucous  membrane.      Draw  a  part  of  the  section  under  the  low  power. 

4.  Sections  of  the  mammary  gland  from  an.  animal  killed  during  lactation. 
Notice  the  fat-globules  in  the  alveoli  and  also  in  the  alveolar  cells.     Draw  an 
alveolus  under  the  high  power. 


The  ovary  is  a  small  solid  organ,  composed  of  a  stroma  of  fibrous 
tissue,  with  many  spindle-shaped  cells,  and  also  containing,  especially 


FIG.  243. — SECTION  OF  THE  OVARY  OF  THE  CAT.     (Schron.)    f. 

1,  outer  covering  and  free  border  of  the  ovary  ;  1',  attached  border ;  2,  the  central  ovarian 
stroma,  showing  a  fibrous  and  vascular  structure  ;  3,  peripheral  stroma  ;  4,  blood- 
vessels ;  5,  Graafian  follicles  in  their  earliest  stages  lying  near  the  surface  ;  6,  7,  8,  more 
advanced  follicles  which  are  embedded  more  deeply  in  the  stroma  ;  9,  an  aimost  mature 
follicle  containing  the  ovum  in  its  deepest  part ;  9',  a  follicle  from  which  the  ovum  has 
fallen  out  in  preparing  the  section  ;  10,  corpus  luteurn. 

O 


210 


THE  ESSENTIALS  OF  HISTOLOGY. 


near  its  attachment  to  the  broad  ligament,  a  large  number  of  plain 
muscular  fibres.  It  is  covered  by  a  layer  of  small  columnar  epithelium- 
cells  (germinal  epithelium,  fig.  244,  a),  between  which  may  here  and 
there  be  seen  a  few  larger  spheroidal  cells,  with  large  round  nuclei 


FIG.  244.— SECTION  OF  THE  OVARY  OF  AN  ADULT  BITCH. 

a,  germ-epithelium ;  b,  egg-tubes  ;  c,  c,  small  follicles ;  d,  more  advanced  follicle ;  e,  discus  pro- 
ligerus  and  ovum;/,  second  ovum  in  the  same  follicle  (this  occurs  but  rarely);  g,  outer 
tunic  of  the  follicle  ;  h,  inner  tunic  ;  i,  membrana  grauulosa  ;  k,  collapsed  retrograded 
follicle  ;  I,  blood-vessels  ;  m.  m,  longitudinal  and  transverse  sections  of  tubes  of  the  paro- 
varium  ;  y,  involuted  portion  of  the  germ-epithelium  of  the  surface ;  2,  place  of  the  transi- 
tion from  peritoneal  to  germinal  or  ovarian  epithelium. 

(primitive  ova,;  fig.  246,  c).     In  the  young  subject  the  epithelium  may 
occasionally  dip  down  into  the  subjacent  stroma. 

The  stroma  is  beset  with  vesicles  of  different  sizes,  the  smallest 
being  near  the  surface  of  the  organ,  the  larger  ones  placed  more  deeply 


GENERATIVE  ORGANS  OF  THE  FEMALE. 


211 


in  the  stroma,  although,   as  they  increase  in  size,  they  may  extend 
towards  the  surface. 

These  vesicles  are  the  Graafian  follicles.  Each  Graafian  follicle  has 
proper  wall  (theca  folliculi)  formed  of  a  layer  derived  from  the  stroma, 
and  contains  an  ovum  and  epithelium.  In  the  smallest  follicles  the 
ovum  is  small,  and  the  epithelium  of  the  follicle  is  formed  of  a  single 
layer  of  cells,  which  are  flattened  against  the  ovum.  In  somewhat 
larger  follicles  the  epithelium-cells  are  in  two  layers,  and  these  are 
columnar  in  shape.  In  still  larger  ones,  each  of  these  two  layers  is 
formed  of  several  strata  of  cells,  and  fluid  has  begun  to  collect  between 
the  layers  at  one  part.  Of  the  two  layers,  the  one  which  lines  the 
cavity  of  the  follicle  is  termed  the  membrana  granulosa,  while  the  mass 
of  cells  which  more  immediately  surrounds  the  ovum  is  known  as  the 
•discus  proligerus. 


FIG.  245. — SEMI-DIAGRAMMATIC  REPKESENTATION  OF  A  MAMMALIAN  OVUM. 
(Highly  magnified.) 

zp,  zona  pellucida  ;  vi,  vitellus ;  gv,  germinal  vesicle  :  gs,  germinal  spot. 

In  the  largest  follicles  the  fluid  has  much  increased  in  amount,  so 
that  the  follicle  has  become  gradually  larger  and  more  tense.  Finally 
it  reaches  the  surface  of  the  ovary,  and  projects  from  that  surface, 
where  it  eventually  bursts,  and  the  liquor  folliculi,  with  its  contained 
ovum,  is  set  free.  This  event  is  believed  to  occur  usually  at  about  the 
time  of  menstruation.1 

The  ova  are  large  spheroidal  cells  (fig.  245),  about  ^T  inch  in 
diameter.  When  mature,  as  in  the  largest  Graafian  follicles,  each  ovum 
is  surrounded  by  a  thick  transparent  striated  membrane  (zona pellucida). 

1  Some  of  the  Graafian  follicles  do  not  burst,  but,  after  attaining  a  certain 
stage  of  maturity,  undergo  a  process  of  retrograde  metamorphosis'aiid  eventually 
•disappear. 


212 


THE  ESSENTIALS  OF  HISTOLOGY. 


Within  this  is  the  protoplasm  of  the  cell  (vitellus),  filled  with  fatty  ami 
albuminous  granules.  Lying  in  the  vitellus,  generally  eccentrically  y 
is  the  large  clear  round  nucleus  (germinal  vesicle),  which  contains  an 
intranuclear  network,  and  usually  one  well-marked  nucleolus  (germinal 
spot).  Both  the  ova  and  the  epithelium  of  the  Graafian  follicles  are 
developed  originally  from  the  germinal  epithelium.  In  the  embryo, 
this  forms  a  thick  layer,  covering  the  fibrous  and  vascular  stroma. 
After  a  time  solid  cords  of  epithelium-cells,  which  in  some  animals  are 
partly  tubular  (ovarian  tubes  of  Pfliiger),  grow  down  into  the  stroma, 
whilst  this  at  the  same  time  grows  into  the  epithelium.  The  cords 
presently  become  broken  up  by  the  ingrowths  of  stroma  into  small 
isolated  nests  of  epithelium-cells,  each  of  which  may  represent  a 


FIG.  246.— SECTION  OF  THE  OVARY  OF  A  NEWLY  BORN  CHILD.     (Waldeyer.) 
(Highly  magnified.) 

a,  ovarian  or  germinal  epithelium  ;  &,  formation  of  an  ovarian  tube  ;  c,  c,  primordial  ova  lyinu 
in  the  germ-epithelium  ;  d,  d,  longer  tube  becoming  constricted  so  as  to  form  nests  of 
cells  ;  e,  e,  larger  nests ;  /,  distinctly  formed  follicle  with  ovum  and  epithelium ;  g,  </. 
blood-vessels. 

Graafian  follicle.  To  form  the  ova,  some  of  the  germinal  epithelium- 
cells  become  enlarged,  and  usually  there  is  one  such  enlarged  cell  in 
each  of  the  isolated  nests.  The  remaining  cells  form  the  epithelium 
of  the  follicle  (see  fig.  246). 

The  stroma  of  the  ovary  contains,  besides  the  spindle-shaped  con- 
nective-tissue cells  and  plain  muscular  fibres  already  mentioned,  a 
number  of  epithelium-like  interstitial  cells,  like  those  found  in  the 
intertubular  tissue  of  the  testis.  They  are  most  abundant  near  the 
hilum.  Corpora  lutea  may  also  be  seen  in  the  stroma.  These  are 
large  yellow  nodules,  which  are  developed  out  of  the  Graafian  follicles 


GENERATIVE  ORGANS  OF  THE  FEMALE. 


213 


after  the  ovum  has  become  extruded.  They  consist  of  columns  of 
large  yellowish  cells,  with  intervening  vascular  fibrous  tissue,  which 
converge  to  a  central  strand  of  connective  tissue  occupying  the  axis  of 
the  nodule.  The  columns  of  cells  are  not  unlike  those  of  the  cortex  of 
the  suprarenal  capsule.  The  corpus  luteum  is  derived  from  the  wall 
of  the  follicle,  which  becomes  thickened  and  folded  by  multiplication 
and  hypertrophy  of  its  cells ;  between  the  folds  connective  tissue  and 
blood-vessels  grow  in  towards  the  centre,  and  in  this  way  the  columnar 
arrangement  above  mentioned  is  produced.  After  persisting  for  a  time 
the  corpus  luteum  gradually  disappears,  its  tissue  becoming  merged 
in  the  surrounding  stroma.  Corpora  lutea  grow  much  larger  and 
remain  much  longer  persistent  in  the  event  of  pregnancy  supervening. 


FIG.  247. — SECTION  ACROSS  THE  FALLOPIAN  TUBE. 

The  Fallopian  tubes  are  lined  by  a  very  vascular  mucous  membrane, 
which  is  covered  with  ciliated  epithelium,  and  has  numerous  longi- 
tudinal folds.  Externally  they  are  covered  by  a  serous  coat,  within 
which  is  a  thin  longitudinal  layer  of  plain  muscular  fibres  overlying 
circular  fibres  of  the  same  tissue. 

The  uterus  is  usually  described  as  composed  of  two  parts,  the  body 
and  cervix.  The  wall  of  the  uterus  is  formed  of  the  following  layers  : 

1.  A  serous  layer,  derived  from  the  peritoneum,  which  covers  the 
greater  part  of  the  fundus. 

2.  A  muscular  layer,  which  is  of  considerable  thickness  and  is  formed 
of  plain  muscular  fibres  disposed  in  two  imperfectly  separated  strata. 
Of   these   the    outer   is   the   true   muscular   coat,    and   its   fibres   are 
arranged  partly  longitudinally,  partly  circularly.     The  inner  muscular 


•2U 


THE  ESSENTIALS  OF  HISTOLOGY. 


layer,  on  the  other  hand,  is  thick  ;  its  fibres  run  in  different  directions, 
but  chiefly  circularly,  and  it  is  prolonged  internally  into  the  deeper  part 
of  the  mucous  membrane,  the  extremities  of  the  uterine  glands  extending 
between  and  amongst  its  fibres.  It  is  imperfectly  separated  from  the 
thinner  external  layer  by  the  ramifications  of  the  larger  blood-vessels, 
and  represents  a  much-hypertrophied  muscularis  mucosoe. 


FIG.  248.— SECTION  OF  THE  MUCOUS  MEMBRANE  OF  THE  BABBIT'S  UTERUS. 

s,  serous  layer;  l.m.,  longitudinal  muscular  fibres;  c.m.,  circular  muscular  fibres  of  the 
muscular  coat ;  a,  areolar  tissue,  with  large  blood-vessels ;  m.m.,  muscularis  mucosse ; 
m,  mucous  membrane. 

3.  A  mucous  membrane,  which  is  very  thick  and  is  composed  of  soft 
connective  tissue  containing  a  large  number  of  spindle-shaped  cells.  It 
contains  long,  simple,  tubular  glands,  which  take  a  curved  or  con- 
voluted course  in  passing  through  the  membrane.  They  are  lined 
by  ciliated  epithelium  continuous  with  that  which  covers  the  inner 
surface  of  the  mucous  membrane.  In  the  cervix  the  mucous  membrane 
is  marked  by  longitudinal  and  oblique  ridges,  and  the  glands  are  shorter 
than  those  of  the  body  of  the  uterus.  Near  the  os  uteri  the  epithelium 
becomes  stratified  and  overlies  vascular  papillae  of  the  corium.  The 
mucous  membrane  is  exceedingly  vascular,  and  it  also  contains  a  large 
number  of  lymphatic  vessels. 


GENERATIVE  ORGANS  OF  THE  FEMALE. 


215 


At  each  menstrual  period  the  greater  part  of  the  mucous  membrane 
of  the  body  undergoes  a  process  of  disintegration  accompanied  by  an 
escape  of  blood  from  the  capillaries  of  the  membrane.  This  is  suc- 
ceeded by  a  rapid  renewal  of  the  membrane.  Should  gestation  super- 
vene, the  process  of  renewal  results  in  the  formation  of  a  greatly 
thickened  mucous  membrane,  with  long  convoluted  glands,  which  is 
then  known  as  the  decidua. 

The  mammary  glands  are  compound  racemose  glands  which  open 
by  numerous  ducts  upon  the  apex  of  the  nipple.  The  ducts  are  dilated 
into  small  reservoirs  just  before  reaching  the  nipple.  If  traced  back- 
wards, they  are  found  as  in  other  compound  racemose  glands  to  com- 
mence in  groups  of  saccular  alveoli.  The  walls  of  the  ducts  and  alveoli 
are  formed  of  a  basement-membrane  lined  by  a  simple  layer  of  flattened 
epithelium  (fig.  249,  A).  But  during  lactation,  when  the  gland  is  in 
activity,  the  cells  of  the  alveoli  become  much  enlarged  and  of  a 
columnar  shape,  and  fatty  globules  become  formed  within  them  (B). 
These  fatty  globules  appear  to  become  set  free  by  the  breaking  down 
of  the  inner  part  of  the  cell,  the  protoplasm  of  the  cells  becoming 


FIG.  249. — ALVEOLI  OF  THE  MAMMARY  GLAND  OF  THE  BITCH  UNDER  DIFFERENT 
CONDITIONS  OF  ACTIVITY.     (Heideiihain. ) 

A,  section  through  the  middle  of  two  alveoli  at  the  commencement  of  lactation,  the  epithelium- 
cells  being  seen  in  profile  ;  B,  an  alveolus  in  full  secretory  activity. 

partially  dissolved  and  forming  the  proteid  substances  of  the  milk. 
According  to  Rauber,  lymph-corpuscles  may  also  carry  fat  into  the 
alveoli  and  there1  become  disintegrated.  At  the  commencement 
of  lactation  the  disintegration  of  the  cells  is  imperfect,  so  that 
numerous  cells  containing  fat-particles  appear  in  the  secretion  (colostrum 
corpuscles). 


216  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  XXXVIII. 

STRUCTURE  OF  THE  SPINAL  CORD. 

SECTIONS  of  the  spinal  cord  from  the  cervical,  dorsal,  and  lumbar  regions. 
As  it  is  difficult  to  obtain  the  human  spinal  cord  sufficiently  fresh,  that  of  a 
dog,  cat,  or  monkey  may  be  used.  It  is  to  be  hardened  by  suspending  it 
immediately  after  removal  from  the  body  in  a  tall  jar  of  Miiller's  fluid  (see 
Appendix).  After  a  few  hours  the  fluid  is  changed,  and  the  cord  is  then  left 
for  about  a  month,  when  it  will  be  ready  for  sections.  These  are  to  be  made 
either  with  the  freezing  microtome  or  by  the  celloidin  method.  They  may 
be  stained  by  the  modified  Pal  method  given  in  the  Appendix,  or  by  aniline 
blue-black.  The  latter  stains  the  nerve-cells  and  axis-cylinders,  the  former 
the  medullary  sheath  of  the  nerve-fibres.  Carminate  of  ammonia  may  also 
be  employed  to  stain  the  nerve-cells  and  axis-cylinders. 

Notice  the  relative  extent  of  the  grey  as  compared  with  the  white  matter 
in  the  different  regions  of  the  cord. 

Sketch  a  section  from  each  region  under  a  low  power.  Sketch  also  a  small 
portion  of  the  white  substance,  two  or  three  nerve-cells,  and  the  central  canal 
with  its  lining  epithelium  and  surrounding  neuroglia  under  the  high  power. 

Measure  the  diameter  of  some  of  the  nerve-fibres  in  the  anterior  columns, 
•n  the  lateral  columns,  and  in  the  posterior  columns. 

2.  Tracts  in  the  spinal  cord.  The  conducting  tracts  of  the  spinal  cord  may 
be  studied  in  two  ways,  viz.  :  (1)  by  preparing  sections  of  embryonic  cords 
(from  the  5th  to  the  9th  month),  the  sections  being  stained  by  the  modified 
Pal  process  ;  (2)  by  preparing  sections  from  the  cord  of  an  animal  in  which 
either  a  complete  section  or  a  hemi -section  has  been  performed  about  10  days 
before  the  animal  is  killed,  and  staining  small  pieces  of  the  cord  from  below 
and  from  above  the  section  by  placing  them  in  a  solution  consisting  of  two 
parts  of  Miiller's  fluid  and  one  part  of  1  per  cent,  osmic  acid  (Marchi's 
method).  The  cord  must  previously  have  been  partly  hardened  by  placing  it 
for  a  few  days  in  Miiller's  fluid. 


The  spinal  cord  is  composed  of  grey  matter  in  the  centre  and  of 
white  matter  externally.  It  is  closely  invested  by  a  layer  of  connective- 
tissue  containing  numerous  blood-vessels  (pia  mater),  arid  less  closely 
by  two  other  membranes.  One  of  these  is  an  areolar  membrane, 
resembling  a  serous  membrane  in  general  structure,  but  non-vascular 
and  more  delicate  in  texture  (arachiioid).  The  other,  which  lines  the 
vertebral  canal,  is  a  strong  fibrous  membrane  known  as  the  dura  mater. 
At  the  middle  of  the  anterior  and  posterior  surfaces  the  pia  mater  dips 
into  the  substance  of  the  cord  in  the  anterior  and  posterior  median 
fissures,  so  as  to  divide  it  almost  completely  into  two  lateral  halves. 


STRUCTURE  OF  THE  SPINAL  CORD. 


217 


FIG.  250. — TRANSVERSE  SECTION  OF  MONKEY'S  SPINAL  CORD.      (Bevan  Lewis.)1 

Cnfrom  the  cervical  region  ;  T,  from  the  thoracic  region  ;  L,  from  the  lumbar  region. 

A,  anterior  cornu  ;  P,  posterior  cornu;  a,  anterior  column  ;  I,  lateral  column  ;  p,  posterior 
column  ;  ac,  anterior  commissure  ;  ae,  ai,  external  and  internal  cell-groups  of  anterior 
cornu  ;  a/,  anterior  median  fissure  ;  ar,  anterior  roots ;  cc,  central  canal  ;  fr,  formatio 
reticularis  ;  il,  lateral  group  of  cells  ;  vc,  vesicular  column  of  Clarke  ;  pc,  posterior  com- 
missure ;  pf,  posterior  median  fissure  ;  pm,  postero-mesial  column ;  pr,  posterior  roots  ; 
sg,  substantia  gelatinosa. 

l  Taken  by  permission  of  the  author  from  Ferrier's  Functions  of  the  Brain.      Second  Edition. 


218 


THE  ESSENTIALS  OF  HISTOLOGY. 


These  are,  however,  united  by  an  isthmus  or  bridge,  which  is  composed 
anteriorly  of  transversely  crossing  white  fibres  (white  commissure), 
posteriorly  of  grey  matter  (grey  commissure),  in  the  middle  of  which  is 
a  minute  canal  lined  by  ciliated  epithelium  (central  canal,  fig.  251,  c.c., 
and  255). 

Each  lateral  half  of  the  spinal  cord  contains  a  crescent  of  grey 
matter,  which  is  joined  to  the  corresponding  crescent  of  the  opposite 
side  by  the  grey  commissure.  Of  the  two  cornua  of  the  crescent  the 
posterior  is  the  narrower  and  comes  near  the  surface  of  the  cord; 
opposite  to  it  the  bundles  of  the  posterior  nerve-roots  enter  the  cord. 
The  bundles  of  the  anterior  nerve-roots  enter  the  anterior  cornu. 

The  white  matter  of  each  half  of  the  cord  is  subdivided  by  the  passage 
of  the  nerve-roots  into  the  cornua  into  three  principal  columns — 
anterior,  lateral,  and  posterior.  In  the  upper  part  of  the  cord  the 


FlG.  251. — A  SMALL  PORTION  OF  A  TRANSVEKSE   SECTION  OP  THE   HUMAN  SPINAL  CORD 

IN  THE  REGION  OF  THE  LATERAL  COLUMN,  TO  SHOW  THE  SUPERFICIAL  NEUROGLIA. 
a,  a,  superficial  neuroglia ;  6,  b,  transverse  section  of  part  of  the  lateral  column  of  the  cord,  in 
which  the  dark  points  are  the  axis-cylinders,  and  the  clear  areas  the  medullary  substance 
of  the  nerve-fibres.  The  superficial  neuroglia  is  seen  to  exhibit  the  appearance  of  a  fine 
network  in  which  numerous  nuclei  and  one  or  two  corpora  amylacea,  are  embedded,  and 
to  extend  inwards  among  the  nerve-fibres. 

posterior  column  is  subdivided  by  a  septum  of  connective  tissue  into 
two — the  postero-mesial  column  or  funiculus  gracilis,  and  the  postero-lateral 
column  or  funiculus  cuneatus.  The  white  matter  is  composed  of  longi- 
tudinally coursing  medullated  nerve-fibres,  which  in  sections  stained 
with  carmine  or  aniline  blue-black  appear  as  clear  circular  areas  with  a 
stained  dot,  the  axis-cylinder,  near  the  middle  (fig.  251);  while  in 
sections  stained  by  the  modified  Pal  method  they  appear  as  black 
circles  with  a  clear  centre.  The  nerve-fibres  vary  in  size  in  different 
parts  ;  on  the  whole  those  which  are  nearest  the  surface  of  the  cord  are 
larger  than  those  nearest  to  the  grey  matter,  but  there  is  a  bundle  of 
very  small  fibres  (M,  fig.  252)  opposite  the  tip  of  the  posterior  horn. 
The  medullated  fibres  are  supported  by  a  peculiar  reticular  tissue 


STKUCTUKE  OF  THE  SPINAL  COED.  219 

(neuroglia)  which  contains  a  number  of  nuclei  embedded  in  it.  These 
nuclei  belong  to  branched  fibrillated  cells  (neuroglia-cells),  of  which 
the  neuroglia  is  wholly  composed.  The  neuroglia  is  accumulated  in 
greater  amount  at  the  surface  of  the  cord  underneath  the  pia  mater 
(fig.  251),  and  it  extends  into  the  grey  matter,  of  which  it  may  be  said 
to  form  the  basis,  and  in  which  it  is  especially  accumulated  at  the  apex 
(caput)  of  the  posterior  cornu  (where  it  forms  the  substantia  gelatinosa  of 
Rolando)  and  around  the  central  canal. 

The  grey  matter,  besides  neuroglia,  consists  of  an  interlacement  of 
nerve-fibres  and  of  the  branching  processes  of  the  nerve-cells  which  are 
embedded  in  it. 

Disposition  of  the  nerve-fibres  of  the  white  columns  in  tracts.— 
The  course  of  the  nerve-tracts  in  the  spinal  cord,  and  in  other  parts  of 
the  central  nervous  system,  can  best  be  made  out  by  the  method  of 
Flechsig,  which  consists  in  the  study  of  sections  of  the  developing 
cord,  for  it  is  found  that  the  formation  of  medullary  substance  occurs 
sooner  in  some  tracts  than  in  others,  so  that  it  is  easy  to  make  out  the 
distinction  between  them.  Another  method  consists  in  investigating 
the  course  which  is  pursued  by  degenerations  of  the  nerve-fibres  in 
consequence  of  lesions  produced  accidentally  or  purposely.  Those 
tracts  in  which  degeneration  of  fibres  occurs  below  the  lesion  are 
termed  "descending"  tracts ;  those  in  which  it  occurs  above  the  lesion 
are  termed  "ascending." 

Investigated  by  these  methods,  it  is  found  that  at  the  posterior 
part  of  the  lateral  column  there  is  a  tract  of  moderately  large  fibres, 
intermingled  with  smaller  fibres,  which  are  found  to  descend  in 
the  lateral  column  of  the  spinal  cord  from  the  opposite  side  of  the 
brain,  after  having  crossed  at  the  pyramids  of  the  medulla  oblongata 
(crossed  pyramidal  tract,  fig.  252).  The  large  fibres  which  lie  in  the 
anterior  columns  next  to  the  anterior  median  fissure,  in  the  upper 
part  of  the  cord,  belong  to  a  portion  of  the  same  tract  which  has 
not  undergone  decussation  (direct  pyramidal  tract).  The  relatively 
small  fibres  of  the  postero-mesial  column  belong  to  a  tract,  known  as  the 
tract  of  Goll  (fig.  252),  which  consists  of  fibres  derived  below  from  the 
posterior  nerve-roots  and  postero-lateral  column,  and  ending  above  in  the 
grey  matter  of  the  funiculus  gracilis  of  the  medulla  oblongata.  The 
postero-lateral  column  itself  (tract  of  Burdach)  is  chiefly  composed  of  the 
fibres  of  the  posterior  nerve-roots  which  run  for  a  short  distance  in  it 
before  entering  the  postero-mesial  column  or  the  grey  matter  of  the  cord. 
The  fibres  of  this  tract  in  the  cervical  region  end  in  the  grey  matter  of 
the  funiculus  cuneatus  of  the  medulla  oblongata.  In  the  lateral 
column  there  are  two  other  ascending  tracts.  One  of  these  is  only 


STRUCTUEE  OF  THE  SPINAL  COED.  221 

distinct  in  the  cervical  and  dorsal  regions.  Here  it  lies  external  to  the 
crossed  pyramidal  tract,  and  consists  of  large  fibres  which  are  derived 
from  the  cells  of  Clarke's  column  (fig.  252,/)  and  pass  up  into  the  cere- 
bellum (dorso-lateral  or  cerebellar  tract).  The  other  one,  situated  more 
anteriorly,  lies  in  front  of  the  crossed  pyramidal  and  direct  cerebellar^ 
tracts  in  the  lumbar  region ;  while  in  the  dorsal  and  cervical  regions  it 
forms  also  a  narrow  band  of  fibres  curving  round  close  to  the  external 
surface  of  the  cord,  and  extending  even  into  the  anterior  column.  This 
is  the  antero-lateral  ascending  tract  of  Gowers.  Its  fibres  are  intermingled 
with  those  of  another  tract  (antero-lateral  descending),  which  degenerates 
(after  section  of  the  cord)  below  the  section,  and  was  first  described  by 
Loewenthal.  Both  this  and  the  ascending  tracts  are  connected  with  the 
cerebellum ;  the  tract  of  Gowers  passing  to  that  organ  over  and  along 
with  the  superior  cerebellar  peduncle,  whilst  the  dorso-lateral  and  the 
descending  enter  with  the  inferior  peduncle.  Lastly,  there  are  two  or 
three  other  small  tracts  of  fibres,  some  of  which  degenerate  above  a  section 
of  the  cord,  others  below.  One  of  these,  an  ascending  tract  (i.e.  under- 
going degeneration  above  the  point  of  section),  is  marked  M  in  the 
figures.  This  is  the  marginal  bundle,  and  is  formed  by  the  fine  fibres 
of  the  posterior  roots  (Lissauer).  Another,  placed  in  the  postero-lateral 
column,  is  the  so-called  comma  tract,  degenerating  for  a  few  centi- 
meters below  the  point  of  section.  Other  small  portions  of  the 
posterior  columns  which  are  marked  in  the  figure  (fig.  252,  P.M'.  and 
s.P.-L.)  are  differentiated  by  the  method  of  Flechsig,  but  their  function 
is  not  known. 

Disposition  of  the  nerve-cells  in  the  grey  matter. — The  nerve-cells 
which  are  scattered  through  the  grey  matter  are  in  part  disposed  in 
definite  groups.  Thus  there  are  two  or  three  groups  of  large  multi- 
polar  nerve-cells  in  the  anterior  cornu;  their  axis-cylinder  processes 
mostly  pass  out  into  the  anterior  nerve-roots  (cells  of  the  anterior  cornu, 
fig.  252,  a,  b,  c).  A  well-marked  group  of  large  rounded  nerve-cells, 
best  marked  in  the  thoracic  region,  lies  at  the  base  of  the  posterior 
cornu  (Clarke's  column,  fig.  252,  /).  The  cells  of  Clarke's  column  send  their 
axis-cylinder  processes  into  the  direct  cerebellar  tract.  Another  group 
is  seen  on  the  outer  side  of  the  grey  matter  lying  in  a  projection  which 
is  sometimes  known  as  the  lateral  cornu  (intermedio-lateral  tract,  fig.  252, 


FIG.  252. — SECTIONS  OF  HUMAN  SPINAL  COED  FROM  THE  LOWER  CERVICAL  (A),  MID- 
DORSAL  (B),  AND  MID-LUMBAR  (C)  REGIONS,  SHOWING  THE  PRINCIPAL  GROUPS  OF 
NERVE-CELLS,  AND  ON  THE  RIGHT  SIDE  OF  EACH  SECTION  THE  CONDUCTING  TRACTS 

AS  THEY  OCCUR  IN  THE  SEVERAL  REGIONS.     (Magnified  about  7  diameters.) 

a,  b,  c,  groups  of  cells  of  the  anterior  horn  ;  d,  cells  of  the  lateral  horn ;  e,  middle  group  of 
cells;  /,  cells  of  Clarke's  column;  g,  cells  of  posterior  horn;  c.c.,  central  canal;  a.c, 
anterior  commissure. 


222  THE  ESSENTIALS  OF  HISTOLOGY. 


STRUCTURE  OF  THE  SPINAL  CORD.  223 

d).  This  is  most  distinct  in  the  upper  dorsal  and  lower  cervical  regions. 
Another  group  (middle  cell-group)  lies  in  the  middle  of  the  crescent  (fig. 
252,  e).  The  cells  of  the  posterior  cornu  (g)  are  not  collected  into  a 
special  group. 

Course  of  the  nerve-roots  in  the  spinal  cord. — The  anterior  roots 
leave  the  anterior  cornu  in  a  number  of  bundles  (fig.  250).  Most 
of  their  fibres  are  directly  continued  from  the  nerve-cells  there. 
On  the  other  hand,  these  cells  are  surrounded  by  an  interlacement 
of  ramified  nerve-endings,  which  are  derived  from  various  sources, 
especially  from  the  collaterals  of  the  posterior  root-fibres  (see  below), 
and  from  those  of  the  descending  fibres  of  the  pyramidal  tracts. 

The  fibres  of  the  posterior  roots  originate  in  the  cells  of  the  posterior 
root  ganglia  (see  diagram,  fig.  253),  and  pass  into  the  postero-lateral 
column,  but  the  smallest  fibres  enter  the  marginal  bundle,  and  some 
pass  into  the  posterior  horn  of  grey  matter.  On  entering  the  spinal 
cord  the  fibres  bifurcate  (diagram,  fig.  253  and  fig.  254),  one  branch 
passing  upwards,  the  other  downwards.  Both  from  the  main  fibre  and 
from  its  branches  collateral  fibres  pass  at  frequent  intervals  into  the 
grey  matter,  and  end  in  arborisations  of  fibrils,  which  envelop  the 
nerve-cells,  both  of  the  posterior  and  of  the  anterior  horn  (see  diagram). 
The  main  fibres  also  for  the  most  part  ultimately  end  in  a  similar  manner 
in  the  grey  matter,  some  after  a  short  course  only,  but  others  after  a 
longer  course.  A  certain  number  of  the  last  named  fibres  pass  upwards 
in  the  postero-lateral  and  postero-mesial  columns  (in  the  latter 
especially  those  of  the  lower  spinal  nerves),  until  they  arrive  at  the 
medulla  oblongata,  where  they  have  a  terminal  arborisation  around  the 
cells  in  the  nucleus  gracilis  and  nucleus  cuneatus. 


FIG.  253. — DIAGRAM  SHOWING  THE  PROBABLE  RELATIONS  OF  SOME  OF  THE  PRINCIPAL 
CELLS  OF  THE  CEREBRO-SPINAL  SYSTEM  TO  ONE  ANOTHER. 

1,  a  cell  of  the  cortex  cerebri ;  2,  its  axis-cylinder  or  nerve-process  passing  down  in  the  pyramidal 
tract,  and  giving  off  collaterals,  some  of  which,  3,  3,  end  in  arborisations  around  cells  of  the 
anterior  horn  of  the  spinal  cord,  the  main  fibre  having  a  similar  ending  at  4  ;  call,  a  collateral 
passing  to  the  corpus  callosum  ;  sir,  another  passing  to  the  corpus  striatum  ;  5,  axis-cylinder 
process  of  anterior  cornu-cell  passing  to  form  a  terminal  arborisation  in  the  end-plate  of  a 
muscle-fibre,  m. 

•<5,  a  cell  of  one  of  the  spinal  ganglia.  Its  axis-cylinder  process  bifurcates,  and  one  branch,  7, 
passes  to  the  periphery  to  end  in  an  arborisation  in  the  sensory  surface,  s.  The  other 
(central)  branch  bifurcates  after  entering  the  cord  (at  8),  and  its  divisions  pass  upwards  and 
downwards  (the  latter  for  a  short  distance  only) ;  9,  ending  of  the  descending  branch  in  a 
terminal  arborisation  around  a  cell  of  the  posterior  horn,  the  axis-cylinder  process  of  which, 
again,  ends  in  a  similar  arborisation  around  a  cell  of  the  anterior  horn;  10,  a  collateral 
passing  from  the  ascending  division  directly  to  envelop  a  cell  of  the  anterior  horn  ;  11,  one 
passing  to  envelop  a  cell  of  Clarke's  column ;  12,  a  collateral  having  connections  like  these 
of  9  ;  13,  ending  of  the  ascending  division  of  the  posterior  root-fibre  around  one  of  the  cells  of 
the  posterior  columns  of  the  bulb ;  14, 14,  axis-cylinder  processes  of  cells  of  the  posterior  horn 
passing  to  form  an  arborisation  around  the  motor  cells  ;  15,  a  fibre  of  the  ascending  cere- 
bellar  tract  passing  up  to  form  an  arborisation  around  a  cell  of  the  cerebellum;  16,  axis- 
cylinder  process  of  this  cell  passing  down  the  bulb  and  cord,  and  giving  off  collaterals  to 
envelop  the  cells  of  the  anterior  horn ;  17,  axis-cylinder  process  of  one  of  the  cells  of  the 
posterior  column  of  the  bulb  passing  as  a  fibre  of  the  fillet  to  the  cerebrum,  and  forming  a 
terminal  arborisation  around  one  of  the  smaller  cerebral  cells ;  18,  axis-cylinder  process  of 
this  cell,  forming  an  arborisation  around  the  pyramidal-cell,  1. 


224 


THE  ESSENTIALS  OF  HISTOLOGY. 


The  central  canal  of  the  spinal  cord  is  lined  by  columnar  ciliated 
epithelium-cells,  which  are  surrounded  by  a  quantity  of  neuroglia. 
The  cells  are  best  seen  in  the  spinal  cord  of  animals  and  in  the  child 
(fig.  255) ;  in  the  human  adult  they  have  frequently  become  proliferated, 
and  their  cilia  are  no  longer  visible. 


FIG.  254.—  FROM  A  LONGITUDINAL  SEC- 
TION OF  SPINAL  COED,  SHOWING  THE 
ENTRANCE  OF  POSTERIOR  ROOT-FIBRES. 

(Earn  on  y  Cajal. ) 

A,  A,  fibres  entering  the  postero-lateral 
column,  and  bifurcating  into  an  ascending 
and  descending  division  ;  B,  C,  collaterals 
passing  from  them  into  the  grey  matter ; 
E,  other  fibres  of  the  posterior  white 
columns  also  giving  off  collaterals. 


FIG.  255.— A,  SECTION  OF  THE  CENTRAL 

CANAL  OF  THE  SPINAL  CORD  OF  A  CHILD, 
SHOWING  ITS  CILIATED  EPITHELIUM 
AND  THE  SURROUNDING  CENTRAL  NEU- 
ROGLIA. (Moderately  magnified.)  B, 
SOME  OF  THE  CILIATED  CELLS.  (Highly 

magnified.) 


Characters  of  the  spinal  cord  in  the  several  regions  (figs.  252,  256). 
In  the  cervical  region  the  white  matter,  especially  that  of  the  lateral 
columns,  occurs  in  largest  proportion.  The  grey  matter,  especially  in 
the  cervical  enlargement,  is  in  considerable  amount  (C  5),  and  it  en- 
croaches in  the  form  of  a  network  upon  the  adjacent  part  of  the  lateral 


STKUCTURE  OF  THE  SPINAL  COED. 


225 


white  column.    The  anterior  cornua  are  thick  and  the  posterior  slender. 
The  postero-mesial  column  is  distinctly  marked  off. 

In  the  dorsal  region  the  grey  matter  is  small  in  amount,  and  both 
cornua  are  slender  (D  5).     The  whole  cord  is  smaller  in  diameter  than 


FIG.  256.— TKANSVEKSE  SECTIONS  OF  THE  SPINAL  CORD  AT  DIFFERENT  LEVELS. 
(Gowers.)    (Twice  the  natural  size.) 

The  letters  and  numbers  indicate  the  position  of  each  section  ;  Ca,  at  level  of  coccygeal  nerve  ; 
Sac.  4  of  4th  sacral;  L3  of  3rd  lumbar,  and  so  on.  The  grey  substance  is  shaded  dark  and 
the  nerve-cells  within  it  are  indicated  by  dots. 

either  in  the  cervical  or  lumbar  region.  The  column  of  nerve-cells 
known  as  Clarke's  column,  and  the  intermedio-lateral  tract,  are  well 
marked. 

In  the  lumbar  region  the  crescents  of  grey  matter  are  very  thick, 
and  the  white  substance,  especially  the  lateral  columns,  relatively  small 


226  THE  ESSENTIALS  OF  HISTOLOGY. 

in  amount  (L  5).  The  isthmus  lies  nearly  in  the  centre  of  the  cord, 
whereas  in  the  cervical  and  dorsal  regions  it  is  nearer  the  anterior 
surface. 

In  the  part  of  the  spinal  cord  from  which  the  sacral  and  coccygeal 
nerve-roots  take  origin  the  grey  matter  largely  preponderates,  the 
crescents  forming  thick  irregular  masses,  and  the  grey  isthmus  is 
also  of  considerable  thickness. 

Blood-vessels  of  the  spinal  cord. — The  blood-supply  of  the  grey 
matter  is  derived  mainly  from  a  series  of  arterioles,  which  come  off 
from  the  mesially-situated  anterior  spinal  artery,  pass  into  the  anterior 
median  fissure,  and  at  the  bottom  of  this  divide  each  into  two  branches, 
one  for  the  grey  matter  of  each  lateral  half  of  the  cord.  In  the  grey 
matter  is  a  very  close  capillary  plexus  which  is  supplied  not  alone  by 
the  vessels  just  mentioned,  but  also  by  small  arterioles,  which  con- 
verge from  the  small  arteries  of  the  pia  mater,  passing  through 
the  white  matter,  and  supplying  this  as  they  pass  through  it.  These 
arterioles  are  branches  of  the  above-mentioned  anterior  spinal  artery 
and  of  the  posterior  spinal  arteries  (which  run  on  each  side  along  the 
line  of  the  posterior  roots).  The  capillary  plexus  of  the  white  matter 
is  far  less  dense  than  that  of  the  grey  matter.  It  forms  longitudinal 
meshes. 

The  veins  of  the  spinal  cord  accompany  the  arteries.  Two  longi- 
tudinal venous  vessels,  accompanying  corresponding  anastomotic 
arterioles  are  seen,  one  on  either  side  of  the  central  canal,  in  most 
transverse  sections  of  the  cord. 


STRUCTURE  OF  THE  MEDULLA  OBLONGATA.  227 


LESSONS  XXXIX.  AND  XL. 

TEE  MEDULLA  OBLONGATA,  PONS,  AND  MESENCEPHALON. 

1.  SECTIONS  of  the  medulla  oblongata  made,  (a)  at  the  level  of  the  decussation 
of  the  pyramids,  (b)  just  above  the  decussation,  (c)  opposite  the  middle  of  the 
olivary  body,  and  (d]  either  through  the  uppermost  part  of  the  olivary  body, 
or  just  above  it. 

2.  Section  through  the  middle  of  the  pons  Varolii. 

3.  Sections  across  the  region  of  the  corpora  quadrigemina,  one  at  the  level 
of  the  inferior,  the  other  at  the  level  of  the  superior,  pair. 

In  all  the  above  sections  sketch  under  a  low  power  the  general  arrange- 
ment of  the  grey  and  white  matter,  inserting  the  positions  of  the  chief  groups 
of  nerve-cells. 

[The  tissue  is  hardened  and  the  sections  are  prepared,  stained,  and  mounted 
in  the  same  way  as  the  spinal  cord.] 


The  structure  of  the  medulla  oblongata  or  bulb  can  best  be  made 
out  by  the  study  of  a  series  of  sections  taken  from  below  upwards,  and 
by  tracing  in  these  the  changes  which  occur  in  the  constituent  parts  of 
the  spinal  cord,  taking  note  at  the  same  time  of  any  parts  which  may 
be  superadded. 

A  section  through  the  region  of  the  decussation  of  the  pyramids 
(fig.  257)  has  much  the  same  form  as  a  section  through  the  upper  part 


FIG.  257.— SECTION  OF  THE  MEDULLA  OBLONGATA 
AT  THE  MIDDLE  OF  THE  DECUSSATION  OF  THE 
PYRAMIDS.  (Lockhart-Clarke.)  f. 

/,  anterior,  f.p.,  posterior  fissure  ;  a.p.t  pyramid  ;  «, 
remains  of  part  of  anterior  cornu,  separated  by  the 
crossing  bundles  from  the  rest  of  the  grey  matter  ; 
I,  continuation  of  lateral  column  of  cord  ;  R,  con- 
tinuation of  substantia  gelatinosa  of  Rolando  ;  p.c. , 
continuation  of  posterior  cornu  of  grey  matter ; 
f.g.,  funiculus  gracilis. 


of  the  spinal  cord,  and  most  of  the  structures  of  the  cord  can  be  easily 
recognised.  A  considerable  alteration  of  the  grey  matter  is,  however, 
produced  by  the  passage  of  the  large  bundles  of  the  crossed  pyramidal 


THE  ESSENTIALS  OF  HISTOLOGY. 


tract  (p)  from  the  lateral  column  of  the  spinal  cord  on  each  side 
through  the  root  of  the  anterior  cornu  and  across  the  anterior  median 
fissure  to  the  opposite  anterior  column  of  the  medulla  oblongata, 
where,  together  with  the  fibres  of  the  direct  pyramidal  tract,  they 
constitute  the  prominent  mass  of  white  fibres  which  is  seen  on  the 
front  of  the  bulb,  on  each  side  of  the  middle  line,  and  is  known  as  the 
pyramid.  By  this  passage  of  fibres  through  the  grey  matter  the  tip  of 
the  anterior  cornu  (a)  is  cut  off  from  the  rest  and  becomes  pushed  as  it 
were  to  the  side  ;  in  sections  a  little  higher  up  it  appears  as  an  isolated 
mass  of  grey  matter  which  is  known  as  the  lateral  nucleus  (fig. 
258,  n.L). 

A  change  also  occurs  in  the  posterior  cornu  in  consequence  of  the 
increased  development  of  the  posterior  column  of  white  matter. 
This  causes  the  posterior  cornua  (fig.  257,  p  c)  to  be  pushed  towards  the 
side,  the  V  which  they  form  with  one  another  being  thus  opened  out ; 
at  the  same  time  the  tip  of  the  cornu  swells  out  and  causes  a  pro- 
minence upon  the  surface  of  the  medulla,  -which  is  known  as  the 
tubercle  of  Rolando  (R).  Grey  matter  also  soon  becomes  found 
within  the  upward  prolongations  of  the  postero-mesial  column  and  of 
the  cuneate  funiculus  (postero-lateral  column,  fig.  258,  n.g.,  n.c.).  But 


/#•   ri.rr. 
f.rn,f.     |        "> 


FIG.  258.— SECTION  OF  THE  MEDULLA 

OBLONGATA  IN  THE  REGION  OF 
THE  SUPERIOR  PYRAMIDAL  DECUS- 

SATION.     (Schwalbe.)    f. 

a.m./.,  anterior'  median  fissure ;  /.a., 
superficial  arciform  fibres  emerging 
from  the  fissure  ;  py.,  pyramid  ;  n.a.r., 
nucleus  of  the  arciform  fibres;  f.a'., 
deep  arciform  fibres  becoming  super- 
ficial ;  o,  lower  end  of  olivary  nucleus  ; 
o',  accessory  olivary  nucleus  ;  n.L,  nu- 
cleus lateralis  ;  f.r.,  formatio  reticu- 
laris  ;  f.a9.,  arciform  fibres  proceeding 
from  formatio  reticularis ;  g,  substantia 
gelatinosa  of  Rolando  ;  a.  V.,  ascending 
root  of  fifth  nerve  ;  n.c.,  nucleus  cunea- 
tus;  n.c'.,  external  cuneate  nucleus; 
f.c.,  funiculus  cuneatus  ;  n.p.,  nucleus 
gracilis  ',f.g.,  funiculus  gracilis ;  p.m.f., 
posterior  median  fissure  ;  c.c.,  central 
canal  surrounded  by  grey  matter,  in 
which  are,  n.XI.,  nucleus  of  the  spinal 
accessory;  and  n.XII.,  nucleus  of  the 
hypoglossal ;  s.d.,  superior  pyramidal 
decussation  (decussation  of  fillet). 


most  of  the  grey  matter  becomes  broken  up,  by  the  passage  of  bundles 
of  nerve-fibres  through  it,  into  a  reticular  formation  (f.r.)  the  pro- 
duction of  which  is  already  foreshadowed  in  the  upper  part  of  the 
spinal  cord.  The  central  canal  of  the  spinal  cord  is  still  seen  in  the 
lower  part  of  the  medulla  oblongata  (c.c.),  but  it  comes  nearer  to  the 


THE  MEDULLA  OBLONGATA. 


229 


posterior  surface.  The  grey  matter  which  surrounds  it  contains  two 
well-marked  groups  of  nerve-cells  ;  the  anterior  of  these  is  the  lower 
part  of  the  nucleus  of  the  hypoglossal  or  twelfth  nerve  (n.  XIL),  the 
posterior  that  of  the  spinal  accessory  or  eleventh  (n.  XL).  Instead  of 
the  comparatively  narrow  isthmus  which  joins  the  two  halves  of  the 
spinal  cord,  a  broad  raphe  now  makes  its  appearance  ;  this  is  formed  of 
obliquely  and  antero-posteriorly  coursing  fibres,  together  with  some 
grey  matter  containing  nerve-cells. 

In  a  section  at  about  the  middle  of  the  olive  (figs.  259,  260),  it  will  be 
seen  that  a  marked  change  has  been  produced  in  the  form  of  the 
medulla  oblongata  and  the  arrangement  of  its  grey  matter,  by  the 
opening  out  of  the  central  canal  into  the  fourth  ventricle.  This 
causes  the  grey  matter  which  lower  down  surrounded  the  central 
canal  to  be  now  spread  out  at  the  floor  of  that  ventricle,  and  the 

FIG.  259. —SECTION  OF  THE  ME- 
DULLA OBLONGATA  AT  ABOUT 
THE  MIDDLE  OF  THE  OLIVARY 

BODY.     (Schwalbe.)    -}-. 

/.Ln.,  anterior  median  fissure  ;  n.ar., 
nucleus  arciformis  ;  p,  pyramid  ; 
XIL,  bundle  of  hypoglossal  nerve 
emerging  from  the  surface  ;  at  6  it 
is  seen  coursing  between  the  pyra- 
mid and  the  olivary  nucleus,  o ; 
f.a.e.,  external  arciform  fibres;  n.L, 
nucleus  lateralis  ;  a,  arciform  fibres 
passing  towards  restiform  body 
partly  through  the  substantia  gela- 
tinosa,  g,  partly  superficial  to  the 
ascending  root  of  the  fifth  nerve, 
aV.  ;  X.,  bundle  of  vagus  root, 
emerging;  /. -/-.  ,formatio  reticularis; 
c.r.,  corpus  restiforme,  beginning 
to  be  formed,  chiefly  by  arciform 
fibres,  superficial  and  deep  ;  n.c., 
nucleus  cuneatus ;  n.g.,  nucleus 
gracilis  ;  t,  attachment  of  the  lig- 
ula  ;  f.s.,  funiculus  solitarius  ;  nX. 
nX'.,  two  parts  of  the  vagus  nu- 
cleus; n.XIf.,  hypoglossal  nucleus ; 
n.t. ,  nucleus  of  the  funiculus  teres  ; 
n.am.  nucleus  ambiguus  ;  ?•,  raphe  ; 
A,  formatio  reticularis  alba;  o',  o", 
accessory  olivary  nuclei ;  o,  olivary 
nucleus;  p.o.L,  pedunculus  olivse. 

collections  of  nerve-cells  from  which  the  hypoglossal  and  spinal 
accessory  nerves  respectively  arose  now,  therefore,  lie  in  a  corre- 
sponding situation.  At  this  level,  however,  the  outer  group  which 
corresponds  with  the  nucleus  of  the  spinal  accessory  in  the  lower 
part  of  the  bulb  has  become  the  nucleus  of  the  vagus  or  tenth 
nerve  (n.X.).  The  nerve-bundles  of  the  roots  of  these  nerves  can 
be  seen  in  the  sections  coursing  through  the  thickness  of  the  bulb 
and  emerging,  those  of  the  hypoglossal  (XIL)  just  outside  the  pyramids, 
those  of  the  spinal  accessory  and  vagus  (X.)  at  the  side  of  the  medulla 
oblongata.  The  two  sets  of  emerging  fibres  thus  appear  to  subdivide 


p.o.i: 


THE  ESSENTIALS  OF  HISTOLOGY. 


each  lateral  half  of  the  bulb  into  three  areas — a  posterior  a  middle, 
and  an  anterior.  Of  these  the  posterior  is  chiefly  occupied  by  the 
grey  matter  of  the  floor  of  the  fourth  ventricle,  and,  with  fibres  which 
are  passing  obliquely  upwards  and  outwards  towards  the  cerebellum, 
forming  its  inferior  crus  (festiform  body,  c.r.);  and  in  addition  there 
is  the  continuation  upwards  of  the  portions  of  grey  matter  forming 
the  nuclei  of  the  funiculus  gracilis  (n.g.),  of  the  funiculus  cuneatus 


aunt. 


FIG.  260.— SECTION  ACROSS  THE  MEDULLA  OBLONG  ATA  AT  ABOUT  THE  MIDDLE  OF 
THE  OLIVARY  BODY.     (Magnified  5  diameters.) 

r  raphe;/,  fillet;  ar.ext..  fibre  arcuatse  extern* ;  n.ar.,  nucleus  arcuatus ;  py,  pyramid; 
n.d.o.,  nucleus  dentatus  olivse  ;  h.o.,  hilum  olivfe ;  s.o.,  siliqua  olivse  ;  acc.o.,  oliva  ac- 
cessoria;  n.L,  nucleus  lateralis ;  ri,  portions  of  grey  matter  containing  large  cells, 


ventral  nucleus  of  tenth  nerve  (nucleus  ambiguus) ;  n.p.,  nucleus  posterior;  s,  fas- 
ciculus solitarius  (ascending  root  of  A',  and  IX.  nerves)  ;  t,  tamia  (attachment  of  ependy- 
mal  roof  of  fourth  ventricle)  ;  /.r.,  formatio  reticularis  ;  n.X.,  dorsal  nucleus  of  tenth 
nerve  ;  n.XIL,  upper  part  of  nucleus  of  twelfth  nerve  ;  n.t.,  nucleus  of  funiculus  teres  ; 
v.l.b.,  posterior  or  dorsal  longitudinal  bundle. 

(n.c.),  and  of  the  tubercle  of  Kolando  (g).  The  anterior  or  mesial  area 
is  occupied  in  front  by  the  pyramid  (p),  and  behind  this  by  a  reticular 
formation  (reticularis  alba,  A)  composed  of  longitudinally  coursing 
bundles  of  fibres  interlaced  with  fibres  that  are  passing  obliquely  from 
the  opposite  side,  through  the  raphe,  towards  the  nuclei  of  the  posterior 
columns  and  restiform  body  (figs.  260,  261).  The  middle  area,  which 
lies  between  the  issuing  bundles  of  the  two  sets  of  nerve-roots,  consists 


THE  MEDULLA  OBLONGATA. 


231 


in  its  deeper  part  of  a  similar  reticular  formation  (figs.  259,  260,  f.r.), 
but  with  more  grey  matter  and  nerve-cells  (reticularis  grisea,  fig.  261, 
r.g.).  Superficially  there  is  developed  within  it  a  peculiar  wavy  lamina 
of  grey  matter  containing  a  large  number  of  small  nerve- cells ;  this  is 
the  dentate  nucleus  of  the  olivary  body  (figs.  259,  260,  n.d.o.).  The  lamina 
is  incomplete  at  its  mesial  aspect  (hilum  olivaB,  fig.  260,  h.o.)}  and  here 
a  large  number  of  fibres  issue,  and  passing  through  the  raphe  course  as 
inner  arcuate  fibres  to  the  opposite  restiform  body,  and  thus  to  the 


r-ff-  XII  r.a 

FIG.  261. — PART  OF  THE  RETICULAR  FORMATION  OF  THE  MEDULLA  OBLONGATA 

(Henle.) 

r.a.,  reticularis  alba,  without  nerve-cells  ;  r.g.,  reticularis  grisea,  with  large  nerve  cells  ; 
between  them  a  root-bundle  of  the  hypoglossus  (XII.).  The  longitudinal  fibres  of  the 
reticular  formation  are  cut  across  ;  the  transversely  coursing  fibres  are  internal  arcuate 
fibres,  passing  on  the  right  of  the  figure  towards  the  raphe. 

cerebellum.  Some,  however,  turn  sharply  round  and  course  below  the 
dentate  nucleus,  forming  an  investment  and  capsule  to  it  (siliqua  oliw, 
fig.  260,  s.o.),  and  pass  towards  the  restiform  body  of  the  same  side. 
Just  dorsal,  or  dorso-lateral  to  the  olive  is  the  continuation  upwards 
of  the  antero-lateral  ascending  tract  of  the  spinal  cord  ;  the  continuation 
of  the  direct  cerebellar  tract  is  now  passing  into  the  restiform  body. 


232 


THE  ESSENTIALS  OF  HISTOLOGY. 


The  floor  of  the  fourth  ventricle  is  covered  by  a  layer  of  ciliated 
epithelium-cells,  continuous  below  with  those  lining  the  central  canal, 
and  above,  through  the  Sylvian  aqueduct,  with  the  epithelium  of  the 
third  and  lateral  ventricles.  The  epithelium  rests  upon  a  layer  of 
neuroglia  known  as  the  ependyma  of  the  ventricle.  The  fourth  ventricle 
is  roofed  over  by  a  thin  layer  of  pia  mater,  with  projecting  choroid 
plexuses,  the  under  surface  of  which  is  covered  by  a  thin  epithelial 
layer  continuous  at  the  side  with  the  ciliated  epithelium  of  the  floor. 
The  roof  becomes  somewhat  thickened  as  it  is  continued  into  the 
ependymal  layer  of  the  floor  of  the  ventricle;  this  thickened  part 
(tcenia  or  ligula,  figs.  259,  260,  t)  is  often  left  attached  when  the  thin 
epithelial  roof  is  removed  along  with  the  pia  mater  which  covers  it. 

n.PZZZp. 


nVlfiai 


FIG.  262. — TRANSVERSE  SECTION  OF  THE  UPPER  PART  OP  THE  MEDULLA 
OBLONGATA.    (Schwalbe. )    £. 

py,  pyramid ;  o,  olivary  nucleus  ;  V.a.,  ascending  root  of  the  fifth  nerve  ;  VIII.,  inferior  (pos- 
terior) root  of  the  auditory  nerve,  formed  of  two  parts,  a,  dorsal,  and  b,  ventral,  which 
enclose  the  restiform  body,  c.r.;  n.  VHLp.,  one  of  the  nuclei  of  the  eighth  nerve;  n.  VIH.ac., 
accessory  nucleus  ;  g,  ganglion-cells  in  the  dorsal  root ;  n.f.t.,  nucleus  of  the  funiculus 
teres  ;  n.XII.,  nucleus  of  the  hypoglossal ;  r,  raphe. 

A  section  taken  through  the  uppermost  part  of  the  olivary  prominence  will 
still  show  very  much  the  same  form  and  structural  arrangements  as 
that  just  described.  The  nucleus  of  the  hypoglossal  (fig.  262,  n.  XII.) 
is  still  visible  in  the  grey  matter  of  the  floor  of  the  ventricle,  but  the 
nerve  which  is  now  seen  arising  from  the  outer  part  of  that  grey 
matter  is  the  eighth  or  auditory  (J^llL),  the  bundles  of  which,  as  they 
leave  the  medulla,  embrace  the  inferior  crus  of  the  cerebellum  (corpus 
restiforme,  c.r.),  which  is  now  passing  into  that  organ.  The  origin  of 


THE  MEDULLA  OBLONGATA.  233 

the  eighth  nerve  is  thus  subdivided  into  two  principal  parts,  known 
respectively  as  the  dorsal  or  lateral  and  the  ventral  or  mesial  roots. 
The  fibres  of  the  dorsal  root  inclose  amongst  them  numerous  ganglion 
cells ;  this  root  becomes  the  cochlear  or  true  auditory  division  of  the 
eighth  nerve.  The  ventral  root,  which  becomes  the  vestibular  division 
of  the  eighth  nerve,  is  connected  with  a  mass  of  grey  matter  mesial  to 
the  restiform  body  (n.VIII.p.\  and  also  with  a  nucleus  (n,VIII.ac.) 
lying  ventral  to  the  restiform  body,  and  known  as  the  accessory 
nucleus.  The  reticular  formation  still  occupies  the  greater  part  of  each 
lateral  half  of  the  bulb  between  the  grey  matter  at  the  floor  of  the 
fourth  ventricle  and  the  pyramids  (py],  and  a  small  portion  of  the 
olivary  nucleus  (o)  may  still  be  seen,  as  may  also  the  upward  continua- 
tion of  the  grey  matter  of  the  tubercle  of  Eolando ;  this  is  intimately 
connected  with  some  well-marked  bundles  of  nerve-fibres,  which  are 
passing  up  to  the  pons  to  join  eventually  the  root  of  the  fifth  nerve 
(Fa).  The  restiform  body  (c.r.)  is  formed  partly  of  the  fibres  of  the 
direct  cerebellar  tract  of  Flechsig  of  the  same  side,  which  are  derived 
below  from  the  cells  of  Clarke's  column,  and  pass  above  into  the  middle 
lobe  of  the  cerebellum,  partly  of  fibres  from  the  opposite  olivary 
nucleus,  and  partly  of  fibres  from  the  olivary  nucleus  of  the  same  side. 
These  pass  to  the  cerebellar  hemisphere  mainly.  It  also  receives  some 
fibres  from  a  nucleus  which  lies  just  outside  the  grey  matter  of  the 
funiculus  cuneatus,  and  is  known  as  the  outer  cuneate  nucleus 
(fig.  258,  n.c'.). 

Pons  Varolii. — A  section  through  the  middle  of  the  pons  Varolii 
(fig.  263)  shows  very  much  the  same  arrangement  of  grey  and  white 
matter  as  that  which  is  met  with  at  the  upper  part  of  the  medulla 
oblongata,  but  the  general  appearance  of  the  section  is  much  modified 
by  the  presence  of  a  large  number  of  transversely  coursing  bundles  of 
nerve-fibres,  most  of  which  are  passing  from  the  hemispheres  of  the 
cerebellum  to  the  raphe  (fibres  of  middle  peduncle  of  cerebellum). 
Intermingled  with  these  bundles  is  a  considerable  amount  of  grey 
matter  (nuclei  pontis).  The  continuation  upwards  of  the  pyramids  of 
the  medulla  (py)  is  embedded  between  these  transverse  bundles  and 
separated  by  them  from  the  reticular  formation.  The  deeper  transverse 
fibres,  those  which  are  nearest  to  the  reticular  formation,  belong  to  a 
different  system  from  those  of  the  middle  peduncle.  They  form  what 
is  known  as  the  trapezium  (fig.  263,  t) ;  a  collection  of  fibres  which  perhaps 
connects  the  superior  olivary  nucleus  (see  below)  of  one  side  with  the 
accessory  auditory  nucleus  (fig.  262,  n.FIII.ac.)  of  the  other  side.  The 
olivary  nucleus  is  no  longer  seen,  but  there  are  one  or  two  small  col- 
lections of  grey  matter  much  more  conspicuous  in  some  animals  than  in 


234 


THE  ESSENTIALS  OF  HISTOLOGY. 


man,  which  lie  in  the  ventral  part  of  the  reticular  formation,  and  are 
known  as  the  superior  olivary  nucleus  (o.s).  The  nerves  which  take 
origin  from  the  grey  matter  of  this  region  are  part  of  the  eighth,  the 
seventh,  the  sixth,  and  somewhat  higher  up  the  fifth  cranial  nerves 
(see  figs.  263,  264).  Of  these  the  eighth  and  fifth  take  origin  from 
groups  of  nerve-cells  which  occupy  the  grey  matter  opposite  the  external 
border  of  the  floor  of  the  ventricle ;  the  sixth  from  a  group  which  is 
placed  also  in  the  grey  matter  of  the  floor  of  the  ventricle  but  nearer 


FIG.  263. — SECTION  ACROSS  THE  PONS  AT  ABOUT  THE  MIDDLE  OF  THE  FOURTH 
VENTRICLE.     (Schwalbe.)     f. 

Pl/>  pyramid-bundles  continued  up  from  the  medulla ;  po,  transverse  fibres  of  the  pons  passing 
from  the  middle  cms  of  the  cerebellum,  before  (po)  and  behind  (po')  the  chief  pyramid 
bundles ;  t,  deeper  fibres  of  the  same  set,  constituting  the  trapezium  ;  the  grey  matter 
between  the  transverse  fibres  is  not  represented  either  in  this  or  in  the  two  following 
figures ;  r,  raphe ;  o.s.,  superior  olivary  nucleus  ;  a.  7.,  bundles  of  the  ascending  root  of 
the  fifth  nerve,  inclosed  by  a  prolongation  of  the  grey  substance  of  Rolando  ;  VI.,  root- 
bundle  of  the  sixth  nerve  ;  n.  VI.,  its  nucleus  ;  VII.,  root-bundle  of  the  facial  nerve  ;  VII.u., 
longitudinal  portion  of  the  same  ;  n.  VII.,  its  nucleus ;  VIII. ,  (superior)  root  of  the  audi- 
tory nerve ;  n.  VIII. ,  its  nucleus  ;  v,  section  of  a  vein. 

the  middle  line,  and  the  seventh  partly  from  a  special  nucleus  which 
lies  in  the  formatio  reticularis,  and  partly  from  the  nucleus  of  the  sixth. 
The  fibres  of  the  nerve  first  pass  backwards  to  the  floor  of  the  ventricle, 
then  longitudinally  upwards  for  a  short  distance,  and  finally  bend 
forwards  and  downwards  to  emerge  between  the  transverse  fibres  at 
the  side  of  the  pons. 

At  the  upper  part  of  the  pons  (fig.  265)  the  fourth  ventricle  narrows 


STRUCTURE  OF  THE  PONS  VAROLIL 


235 


FIG.  264.— OBLIQUE  SECTION 

OF  THE  PONS  ALONG  THE 
LINE  OF  EXIT  TRAVERSED 
BY  THE  FIFTH  NERVE,  f. 
The  section  passes  through  the 
lower  part  of  the  motor  nu- 
cleus (n'v)  from  which  a  bundle 
of  fibres  of  the  motor  root  is 
seeu  passing,  V't  a  part  of  the 
upper  sensory  nucleus  (nv)  is 
also  shown  in  the  section  in  the 
form  of  a  number  of  small  iso- 
lated portions  of  grey  matter. 
Amongst  these  are  a  few 
bundles  of  the  ascending  root 
cut  across,  but  most  of  these 
have  already  become  diverted 
outwards  to  join  and  assist  in 
forming  the  issuing  part  of  the 
main  or  sensory  root,  V',  I, 
small  longitudinal  bundle  of 
fibres  near  the  median  sul- 
cus  (m.s.),  passing  outwards 
to  join  the  root  of  the  fifth 
nerve;  /.?•.,  formatio  reticu- 
laris;  r,  raphe;  s.f.,  substan- 
tia  ferruginea. 


\ 


FIG.  265. — TRANSVERSE  SECTION  THROUGH  THE  UPPER  PART  OF  THE  PONS. 
(Schwalbe.)     (Rather  more  than  twice  the  natural  size.)1 

p,  transverse  fibres  of  the  pons  ;  py,  py,  bundles  of  the  pyramids  ;  a,  boundary  line  between 
the  tegmental  part  of  the  pons  and  its  ventral  part ;  I',  oblique  fibres  of  the  fillet,  passing 
towards  /,  £2,  longitudinal  fibres  of  the  fillet;  /.?•.,  formatio  reticularis;  p.L,  posterior 
longitudinal  bundle;  s.c.p.,  superior  cerebellar  peduncle;  v.»i.,  superior  medullary  velum; 
b,  grey  matter  of  the  lingula  ;  r.  4,  fourth  ventricle  ;  in  the  grey  matter  which  bounds  it 
laterally  are  seen,  d.  V.,  the  descending  root  of  the  fifth  nerve,  with  its  nucleus;  s.f.,  sub- 
stantia  ferruginea;  g.c.,  group  of  cells  continuous  with  the  nucleus  of  the  aqueduct. 


i  The  details  of  this  and  of  several  of  the  preceding  figures  are  filled  in  under  a  somewhat  higher 
magnifying  power  than  that  used  for  tracing  the  outlines. 


236 


THE  ESSENTIALS  OF  HISTOLOGY. 


considerably  towards  the  Sylvian  aqueduct,  and  behind  and  on  either 
side  of  it  two  considerable  masses  of  longitudinal  white  fibres  make 
their  appearance.  These  are  the  superior  crura  of  the  cerebellum  (s.c.p.) 


FIG.  266.— SECTIONS  THROUGH  THE  ORIGIN  OF  THE  FOURTH  NERVE.    (Schwalbe.)    f. 

A,  transverse  section  at  the  place  of  emergence  of  the  nerve  fibres.  B,  oblique  section 
carried  along:  the  course  of  the  bundles  from  the  nucleus  of  origin  to  the  place  of  emer- 
gence. Aq,  Sylvian  aqueduct,  with  its  surrounding  grey  matter  ;  IV,  the  nerve-bundles 
emerging  ;  IV,  decussation  of  the  nerves  of  the  two  sides  ;  IV",  a  round  bundle  passing 
downwards  by  the  side  of  the  aqueduct  to  emerge  a  little  lower  down  ;  n.lV.,  nucleus  of 
the  fourth  nerve.  I,  fillet;  s.c.p.,  superior  cerebellar  peduncle;  dV,  descending  root  of 
the  fifth  nerve  ;  pi,  posterior  longitudinal  bundle  ;  r,  raphe. 

and  they  tend  as  they  pass  upwards  gradually  to  approach  the  middle 
line  (fig.  266,  A),  across  which  in  the  region  of  the  posterior  pair  of  the 
corpora  quadrigemina  they  pass,  decussating  with  one  another,  to  the 
formatio  reticularis  of  the  opposite  side  (figs.  267,  A,  268). 

The  antero-lateral  ascending  tract  of  the  spinal  cord  is  continued  up 
through  the  ventral  part  of  the  pons  Varolii  lateral  to  the  pyramid- 
bundles,  but  at  about  the  level  of  the  exit  of  the  fifth  nerve  its  fibres 
begin  to  pass  obliquely  towards  the  dorso-lateral  part  of  the  pons, 
where  the  superior  cerebellar  peduncle  is  emerging  from  the  cerebellar 
hemisphere.  The  tract  in  question  now  curves  over  the  lateral  aspect 
of  this  peduncle,  and  then  takes  a  sharp  backward  turn,  passing  over 


FIGS.  267,  268. — OUTLINE  OF  TWO  SECTIONS  ACROSS  THE  MESENCEPHALON. 
(Natural  size.) 

267,  through  the  middle  of  the  inferior  corpora  quadrigemina.  208,  through  the  middle  of 
the  superior  corpora  quadrigemina.  cr,  crusta  ;  s.n.,  substantia  nigra  ;  t,  tegmentum  ;  s, 
Sylvian  aqueduct,  with  its  surrounding  grey  matter  ;  c.q. ,  grey  matter  of  the  corpora  quad- 
rigemina ;  l.g.,  lateral  groove  ;  p.L,  posterior  longitudinal  bundle  ;  d.  V.,  descending  root  of 
the  fifth  nerve  ;  s.c.p.,  superior  cerebellar  peduncle  ;  /,  fillet ;  n.IIL,  its  nucleus ;  ///.,  third 
norve.  The  dotted  circle  in  B  indicates  the  situation  of  the  tegmental  nucleus. 


STRUCTURE  OF  THE  MESENCEPHALON. 


237 


its  dorsal  aspect  to  enter  the  middle  lobe  of  the  cerebellum  in  the 
superior  medullary  velum. 

Mid-brain  or  Mesencephalon. — In  sections  across  the  mesencephalon 
(figs.  267,  268,  269),  the  upward  continuity  of  the  parts  which  have 
thus  been  described  in  the  lower  parts  of  the  nerve-centres,  can  still 
in  great  measure  be  traced. 


FIG.  269.— SECTION  ACROSS  THE  MID-BRAIN  THROUGH  THE  INFERIOR  PAIR  OF 
CORPORA  QUADRIGEMINA.     (Magnified  about  3J  diameters.) 

Sy,  aqueduct  of  Sylvius  ;  c.ctr.,  central  grey  matter  of  the  aqueduct ;  n.III.lV.,  group  of 
cells  forming  part  of  the  conjoined  nucleus  of  the  third  and  fourth  nerves  ;  c.q.p.,  one 
of  the  posterior  corpora  quadrigemina ;  gr,  median  groove  separating  it  from  that  of 
the  opposite  side;  str.l.,  stratum  lemnisci  (layer  of  the  fillet),  forming  its  superficial 
layei- ;  /,  upper  fillet ;  /',  lateral  fillet ;  d'.  V,  descending  root  of  fifth  nerve  ;  p.l.b.,  pos- 
terior longitudinal  bundle;  f.r.t.,  foi-matio  reticularis  tegmenti  ;  d,  d',  decussating 
fibres  of  tegmenta ;  s.c.p.,  superior  cerebellar  peduncle;  p.p.,  pes  pedunculi  (crusta); 
s.n.,  substantia  nigra  ;  g.i.p.,  interpeduncular  grey  matter. 

The  Sylvitin  aqueduct  (fig.  269,  Sy),  with  its  lining  of  ciliated  epithe- 
lium, represents  the  central  canal  of  the  cord  and  the  fourth  ventricle 
of  the  medulla  oblongata.  In  the  grey  matter  which  surrounds  it  (central 
grey  matter)  there  is  seen  in  all  sections  of  the  region  a  group  of  large 
nerve-cells  lying  anteriorly  on  each  side  of  the  middle  line,  close  to  the 


238  THE  ESSENTIALS  OF  HISTOLOGY. 

reticular  formation.  From  this  group  the  root-bundles  of  the  fourth 
nerve  arise  at  the  lower  part  of  the  mesencephalon  and  pass  obliquely 
backwards  and  downwards  around  the  central  grey  matter,  decussating 
with  those  of  the  opposite  side  to  emerge  just  above  the  pons  Varolii 
(fig.  266).  Higher  up,  the  bundles  of  the  third  nerve  spring  from  the 
continuation  of  the  same  nucleus  (fig.  268,  n.  ni.),  and  these  pass 
forwards  and  downwards  with  a  curved  course  through  the  reticular 
formation,  to  emerge  at  the  mesial  side  of  the  crusta. 

The  reticular  formation  of  the  pons  is  continued  up  into  the  mes- 
encephalon, and  is  here  known  as  the  tegmentum.  It  is  composed  as 
before  of  longitudinal  and  transverse  bundles  of  fibres  with  much  grey 
matter  intermingled.  The  transverse  fibres  include  the  decussating 
fibres  of  the  superior  crura  of  the  cerebellum  (s.c.p.),  and  the  fibres  of  the 
Jillet  (/),  which  are  passing  in  an  oblique  manner  from  the  raphe  to  the 
side  of  the  mesencephalon,  to  reach  eventually  the  grey  matter  of  the 
prominences  of  the  corpora  quadrigemina.  The  pyramid  bundles  of  the 
pons  are  continued  upwards  on  each  side  into  the  crusta  (figs.  267,  268, 
cr.,  fig.  269,  p.p.).  This  forms  a  mass  of  longitudinally  coursing  bundles 
of  fibres  lying  on  the  ventral  aspect  of  each  half  of  the  mesencephalon,  and 
diverging  above  into  the  internal  capsule  of  the  cerebral  hemisphere. 
The  crusta  is  separated  from  the  tegmentum  by  a  layer  of  grey 
matter  containing  a  number  of  very  deeply  pigmented  nerve-cells 
which  give  it  the  name  of  substantia  nigra  (s.n.).  The  crusta  and 
tegmentum,  together  with  the  intervening  substantia  nigra,  constitute 
the  crus  cerebri. 

The  prominences  of  the  corpora  quadrigemina  are  formed  mainly  of 
grey  matter  containing  numerous  nerve-cells.  From  each  a  bundle 
of  white  fibres  (brachium)  passes  upwards  and  forwards  towards 
the  geniculate  bodies,  eventually  joining  the  optic  tract  of  the  same 
side.  On  the  other  hand,  each  of  the  prominences  receives  from  below 
fibres  of  the  fillet,  which  are  traceable  below  into  the  ventral  part  of  the 
anterior  area  of  the  medulla  oblongata,  and  then  through  the  raphe  to 
the  nuclei  of  the  gracile  and  cuneate  funiculi  of  the  opposite  side. 
Since  these  nuclei  contain  the  terminal  arborisations  of  many  of  the 
ascending  fibres  of  the  posterior  spinal  roots  (see  diagram,  p.  222),  and 
the  fibres  of  the  fillet  emanate  from  cells  in  the  nuclei,  the  fillet  forms  a 
second  link  in  the  chain  of  afferent  fibres  leading  towards  the  brain. 
Some  of  the  fibres  of  the  fillet  are  continued  up  beyond  the  mid-brain 
into  the  subthalamic  region  of  the  cerebrum.  The  superior  corpora 
quadrigemina  receive  many  of  the  fibres  of  the  optic  tract  which  form 
a  superficial  white  stratum  covering  the  grey  matter.  These  fibres  are 
derived  from  nerve-cells  in  the  retina  (diagram,  fig.  270),  and  having 


STRUCTURE  OF  THE  MESENCEPHALON. 


239 


arrived  at  the  superior  quadrigeminal  body  and  formed  the  stratum 
in  question,  they  turn  into  the  grey  matter  and  end  in  arborisations. 
The  cells  of  the  grey  matter  of  this  body  are  very  various  in  form 


rtcx  cerelri 


FIG.  270.— DIAGRAM  OF  THE  PROBABLE  RELATIONS  OF  SOME  OF  THE  NERVE-CELLS  AND 
FIBRES  BELONGING  TO  THE  RETINAL  AND  CENTRAL  VISUAL  APPARATUS. 

and  size,  and  are  disposed  in  several  layers,  which  are  better  seen 
in  the  optic  lobe  of  the  bird  than  in  mammals.  Most  of  their  axis- 
cylinder  processes  pass  ventralward.  Their  destination  is  not  certainly 
known,  but  some  appear  to  pass  downwards  with  the  fillet,  whilst 
others  probably  turn  upwards  and  run  in  the  tegmentum  towards  the 
higher  parts  of  the  brain ;  whilst  others,  perhaps  most,  probably  form 
terminal  arborisations  around  the  motor  cells  of  the  oculomotor  of 


MO  THE  ESSENTIALS  OF  HISTOLOGY. 

other  motor  nuclei.  All  the  nerve-fibres  of  the  optic  nerve  and  optic 
tract  do  not  enter  the  corpora  quadrigemina.  Some  pass  into  the 
lateral  geniculate  bodies  and  form  arborisations  here.  On  the  other 
hand,  from  the  cells  of  these  geniculate  bodies  the  axis-cylinder  pro- 
cesses appear  to  pass  to  the  cortex  of  the  brain  (occipital  region).  The 
probable  relations  of  some  of  these  fibres  and  cells  of  the  nervous  visual 
apparatus  is  indicated  in  the  annexed  diagram  (fig.  270). 


STRUCTURE  OF  THE  CEREBELLUM. 


•241 


LESSON  XLL 


STRUCTURE  OF  THE  CEREBELLUM  AND  CEREBRUM. 

1.  SECTIONS  of  the  cerebellum  vertical  to  the  surface,  (a)  across  the  direction 
of  the  laminae,  (6)  parallel  with  the  laminae. 

2.  Section  across  the  whole  of  one  hemisphere  of  the  cerebrum  of  a  monkey, 
passing  through  the  middle  of  the  third  ventricle. 

3.  Vertical  sections  of  the  cerebral  cortex,  one  from  the  ascending  frontal 
gyms,  another  from  the  occipital  lobe,  and  a  third  across  the  hippocampal 
gyrus  and  hippocampus. 

4.  Transverse  sections  of  the  olfactory  tract  and  bulb. 

In  all  these  preparations  make  sketches  under  a  low  power  of  the  general 
arrangement  of  the  grey  and  white  matter,  and  also  of  the  nerve-cells  in  the 
grey  matter.  Sketch  some  of  the  details  under  a  high  power. 

[The  preparations  are  made  in  the  same  way  as  those  of  the  spinal  cord.] 


The  cerebellum  is  composed  of  a  white  centre,  and  of  a  grey  cortex, 
both  extending  into  all  the  folds  or  laminae,  so  that  when  the  laminae 
are  cut  across,  an  appearance  is  presented  of  a  white  arborescence 


Fiu.  271.— SECTION  THROUGH  ONE  OF  THE  HEMISPHERES  OF  THE  CEREBELLUM  ACROSS 

THE  LAMELL.E,   TO  SHOW  THE  MEDULLARY  CENTRE  AND  ITS   PROLONGATIONS   INTO 
THE  LAMELLJS. 

covered  superficially  by  grey  matter.     The  white  matter  is  in  largest 
amount  in  the  middle  of  each  cerebellar  hemisphere  (fig.  271).     There 

Q 


242 


THE  ESSENTIALS  OF  HISTOLOGY. 


is  here  present  a  peculiar  wavy  lamina  of  grey  matter,  similar  to  that 
in  the  olivary  body,  and  known  as  the  nucleus  dentatus  (n.d.).  Other 
isolated  grey  nuclei  lie  in  the  white  matter  of  the  middle  lobe. 

The  grey  matter  of  the  cerebellum  consists  of  two  layers  (fig.  272). 
The  inner  one  (that  next  the  white  centre)  is  composed  of  a  large 
number  of  very  small  nerve-cells  intermingled  with  a  few  larger  ones 


FIG.  272. — SECTION  OF  CORTEX  OF  CEREBELLUM.     (Sankey.) 

«,  pia  mater  ;  b,  external  layer  ;  c,  layer  of  corpuscles  of  Purkin  je  ; 

d,  inner  or  granule  layer ;  e,  medullary  centre. 

and  some  neuroglia-cells  (granule  layer,  d).  The  outer  layer  (b)  is 
thicker,  and  is  formed  of  neuroglia,  with  rounded  and  angular  small 
nerve-cells  and  neuroglia-cells  scattered  through  it.  Into  its  outer  part 
processes  of  the  pia  mater  conveying  blood-vessels  pass  vertically,  and 
there  are  also  in  this  part  a  number  of  long  tapering  cells,  somewhat 


STRUCTURE  OF  THE  CEREBELLUM. 


243 


like  the  Miillerian  fibres  of  the  retina.  Lying  between  the  two  layers 
of  the  grey  matter  is  an  incomplete  stratum  of  large  flask-shaped  cells 
(cells  of  Purkinje,  c).  Each  of  these  gives  off  from  its  base  a  fine 
process,  which  becomes  the  axis-cylinder  of  one  of  the  medullated  fibres 
of  the  white  centre,  while  from  the  opposite  pole  of  the  cell  large 
ramified  processes  spread  out  into  the  superficial  layer  of  the  grey 
matter  (dendrites}. 


H-4  e 


The  dendrites  of  the  cells  of  Purkinje  spread  out  in  planes  transverse 
to  the  direction  of  the  lamellae  of  the  organ,  so  that  they  present 
a  different  appearance  according  to  whether  the  section  is  taken  across 
the  lamellae  or  along  them  (compare  fig.  273,  I.  and  II.).  These 
dendrites  are  invested  at  their  attachment  to  the  cell,  and  for  some 


244 


THE  ESSENTIALS  OF  HISTOLOGY. 


FIG.  274. — BASKET-WORK  OF  FIBRES  AROUND  TWO  CELLS  OF 
PURKLNJE.     (Ramon  y  Cajal.) 

a,  axis-cylinder  or  nerve-fibre  process  of  one  of  the  corpuscles 
of  Purkinje  ;  b,  fibres  prolonged  over  the  beginning  of  the 
axis-cylinder  process  ;  c,  branches  of  the  nerve-fibre  pro- 
cesses of  cells  of  the  molecular  layer,  felted  together 
around  the  bodies  of  the  corpuscles  of  Purkinje. 


FIG.  275. — TRANSVERSE  SECTION  OF  A  CEREBELLAR  LAMELLA  OF  THE  ADULT  RAT 

SHOWING   THE   FIBRES   WHICH    PASS    FROM  THE   WHITE   CENTRE   TO   THE   GREY 

MATTER.     (Ramon  y  Cajal.) 

A,  molecular  layer  ;  B,  level  of  cells  of  Purkinje  ;  C,  granule  layer ;  D,  white  substance. 

«»  f ,  ft  ff>  fibres  which  end  in  basket-work  arborisations,  b,  enveloping  the  dendrite* 
of  Purkinje's  cells  ;  c,  body  of  cell  of  Purkinje  ;  o,  probably  an  axis-cylinder  pro- 
cess from  one  of  the  cells  of  Purkinje  ;  in,  "  moss  "  fibres  ramifying  in  the  granule 
layer. 


STRUCTURE  OF  THE  CEREBRUM.  245 

extent  along  their  branchings,  by  a  basket-work  formed  of  the  terminal 
arborisation  of  some  of  the  fibres  of  the  medullary  centre  other  than 
those  which  are  continuous  with  the  axis-cylinder  processes  of  the  same 
cells  (fig.  275).  The  body  of  the  cell  of  Purkinje  is  further  invested 
by  a  felt-work  of  fibrils  formed  by  the  arborisation  of  axis-cylinder 
processes  of  nerve-cells  in  the  outer  layer  of  the  grey  matter  (fig.  274). 
Each  cell  has  therefore  a  double  investment  of  this  nature,  one  covering 
the  dendrites,  the  other  the  body  of  the  cell. 

The  granules  of  the  inner  layer  of  grey  matter  are  mostly  small 
nerve-cells,  with  a  few  extended  dendrites  penetrating  amongst  the 
other  granules,  and  an  axis-cylinder  process  which  is  directed  between 
the  cells  of  Purkinje  into  the  outer  layer.  After  penetrating  a  greater 
or  less  distance  into  this  layer  it  bifurcates,  and  its  two  branches  pass 
in  opposite  directions  at  right  angles  to  the  main  stem,  and  parallel 
to  the  direction  of  the  lamella  (fig.  273,  I.).  What  ultimately  becomes 
of  them  is  not  known.  In  sections  cut  across  the  lamellae  the  cut  ends 
of  these  fibres  give  a  finely  punctated  appearance  to  the  outer  layer 
(fig.  273,  II.). 

Ramifying  amongst  the  cells  of  the  granule-layer  are  peculiar  fibres 
derived  from  the  white  centre,  and  characterised  by  having  tufts  of  fine 
short  branches  at  intervals  like  tufts  of  moss  (fig.  275,  m).  These  are 
termed  by  Cajal  the  moss-fibres ;  they  end  partly  in  the  granule  layer, 
partly  in  the  molecular  layer. 

Structure  of  the  cerebrum.— The  grey  matter  of  the  cerebral  cortex 
is  described  as  being  composed  of  a  number  of  layers,  but  they  are  not 
sharply  marked  off  from  one  another,  and  they  vary  in  relative  develop- 
ment in  different  regions  of  the  cortex.  The  following  are  usually 
distinguished. 

1.  A  thin    peripheral   stratum    (molecular   layer)   containing   a   few 
scattered  cells,  which  are  mostly  neuroglia-cells.     They  tend  to  take  a 
direction  vertical  to  the  surface  (fig.  276).      In  the  most  superficial 
part  of  this  layer,  immediately  under  the  pia  mater,  is  a  thin  stratum 
of  medullated  nerve-fibres,  and  besides  these  the  layer  contains  a  large 
number  of  non-medullated  fibres,  many  of  which  are  ramified.     They 
.are  derived  from  the  nerve-processes  of  some  of  the  deeper  nerve-cells 
of  the  cortex.     Intermingled  with  these  fibres  are  a  certain  number  of 
ramified  nerve-cells,  most  of  which  have  two  (sometimes  three)  axis- 
cylinder  processes,  all  of  which  terminate  by  arborisation  within  the 
•superficial  layer. 

2.  A  layer  of  closely  set  small  pyramidal  nerve-cells  several  deep 
(layer  of  small  pyramid*). 

3.  A  layer  of  medium-sized   pyramidal  cells  less  closely  set,  with 


246  THE  ESSENTIALS  OF  HISTOLOGY. 

small  granular-like  cells  amongst  them  (layer  of  larger  pyramids).     The 
pyramidal  cells  are  larger  in  the  deeper  parts  of  the  layer. 

4.  A  layer  of  small  irregular  polymorphous  cells.      In  the   psycho- 
motor  region  of  the  cortex  (portions  of  the  frontal  and  parietal  lobes) 
pyramidal  cells  of  very  large  size  extend  amongst  these  polymorphous 
cells,  and  are  disposed  in  small  clusters  or  "  nests  "  (Be van  Lewis,  Betz) 
(figs.  279,  280). 

5.  A  layer  of  small  scattered  cells,  many  of  a  fusiform  shape.     This 
layer  lies  next  to  the  white  centre.     It  is  not  always  distinct  from  the 
polymorphous  layer.    In  the  island  of  Reil  this  stratum  is  considerably 
developed,  and  is  separated  from  the  rest  of  the  grey  matter  by  a  layer 
of  white  substance.     It  is  here  known  as  the  daustrum  (see  fig.  285,  d.). 

From  the  white  centre  bundles  of  medullated  nerve-fibres  pass  in 
vertical  streaks  through  the  deeper  layers  of  the  grey  matter,  to  lose 
themselves  amongst  the  pyramidal  cells  of  the  more  superficial  layers. 
Some  of  these  fibres  are  continuous  with  the  axis-cylinder  processes  of 
the  pyramidal  and  polymorphous  cells,  and  therefore  take  origin  in  the 
cortex ;  others  are  passing  into  the  cortex  to  end  amongst  the  cells  of 
the  several  layers  in  free  arborisations.  The  axis-cylinder  processes  of 
the  pyramidal  cells  pass  into  the  white  centre.  Here  some  of  them  are 
continued  either  directly  or  by  collaterals  into  the  corpus  callosum, 
and  go  through  this  to  the  cortex  of  the  opposite  hemisphere  (comwiv- 
sural  fibres) ;  others  join  association  fibres  which  run  longitudinally  or 
transversely,  eventually  to  pass  again  into  the  grey  matter  of  other 
parts  of  the  same  hemisphere ;  whilst  others  again,  especially  those  of 
the  largest  pyramidal  cells,  extend  downwards  through  the  corona, 
radiata  and  internal  capsule,  and  become  fibres  of  the  pyramidal  tract 
(projection  fibres).  As  they  pass  down  through  the  white  matter  of  the 
hemisphere  they  give  off  collateral  fibres  to  the  corpus  callosum  and 
to  the  basal  ganglia  (corpus  striatum  and  optic  thalamus)  (see  diagram, 
fig.  253,  p.  222). 

There  is,  as  already  stated,  a  great  amount  of  variation  met  with  in 
the  relative  extent  of  development  of  the  above  layers.  Some  of  these 
variations  are  exemplified  in  the  accompanying  drawings  of  preparations 
from  the  monkey's  cerebral  cortex  by  Bevan  Lewis.  From  these  it  will 
be  seen  that  smaller  sized  cells  prevail  in  the  sensory  regions  of  the 
cortex  (occipital,  temporal) ;  larger  and  fewer  cells  occur  in  the  psycho- 
motor  parts.  The  structure  of  the  hippocampal  region  presents  so 
many  peculiarities  as  to  necessitate  a  special  description. 

In  the  hippocampus  major  and  hippocampal  gyrus  (fig.  283)  the 
superficial  layer  of  neurolgia  and  the  white  stratum,  which  overlies  it 
as  a  thin  band  in  other  parts  of  the  cortex,  are  both  very  strongly 


STRUCTURE  OF  THE  CEREBRUM. 


247 


FIG.  276. — SECTION  OF  CEREBRAL  CORTEX  OF  YOUNG  RABBIT,  PREPARED  BY 

GOLGl'S  METHOD.       (G.  RetziuS.) 

g,  pyramidal  cells  of  second  and  third  layer  sending  their  axis-cylinder  processes, 
a,  a,  towards  the  white  centre  ;  d,  d,  dendrites  of  pyramids  ;  p,  polymorphous 
cell  of  fourth  layer,  with  its  axis-cylinder  extending  towards  the  surface  ;  n,  n, 
neuroglia-cells. 


248 


THE  ESSENTIALS  OF  HISTOLOGY. 


i^lf^WT" 

•*•"*    -41  *£'•    **#   * 


Fiu.  277.—  SECTION  OF  COR- 

TEX  OF  OCCIPITAL  LOBE. 


1,  peripheral  layer;  2,  small 
angular  ceUs;  3,  pyramidal 
cells;  4,  angular  and  granule 


cells  ;  5,  pyramidal  cells  ;  6, 
granules  and  ganglionic 
cells  ;  7,  spindle-cells. 


FIG.  278.—  SECTION  OF  COR- 
TEX  OF  TEMPORAL  LOBE. 

1,  peripheral  layer;  2,  small 
angular  cells;  3,  pyramidal 
cells;  4,  granular  layer;  5, 
ganglionic  cells  ;  6,  spindle- 
cells. 


FIG.  279.—  SECTION  OF  COR- 
TEX OF  FRONTAL  LOBE. 

1,  peripheral  layer;  2,  small 
angular  cells  ;  3,  large  pyra- 
midal  cells;  4,  ganglionic 
cells  ;  5,  spindle-cells. 


STRUCTURE  OF  THE  CEREBRUM. 


249 


1 


M 


/?:-;V*(  ' 


*  ,  / 


*'  ••'     •   •*"'•   '•' 


FIG.  280.— SECTION  OF  COR-  FIG.   281.  —  SECTION   OF  FIG.  282.— SECTION  OF  COR- 
TEX OF  MOTOR  AREA.  HIPPOCAMPUS  MAJOR.  TEX  OF  GYRUS  HIPPO- 

1,  peripheral  layer;  2,  small  1,    granular    stratum    of    fascia  CAMPI. 

angular  cells ;  3,  large  pyra-  dentata  ;    2,    nuclear    lamina  ;  j    peripheral  layer  ;  2,  aggre- 

midal  cells;    4.  ganglionic  3,     stratum     laciniosum ;      4,  'gated    pyramidal    cells;    3, 

cells  and  '  cell-clusters '  ;  5,  stratum    radiatum  ;     5,     gan-  large  pyramidal  cells, 

spindle-cells.  glionic    layer ;     6,    molecular 
stratum;    7,  alveus. 

Figs.  277  to  282  are  taken  by  the  author's  permission  from  Ferrier's  Functions  of  the 
Brain,  2nd  edition.  They  are  from  preparations  and  drawings  (from  the  monkey's  brain) 
made  by  Mr.  Bevan-Lewis,  and  are  magnified  about  145  diameters. 


250 


THE  ESSENTIALS  OF  HISTOLOGY. 


marked  (5,  6),  the  neuroglia-layer  having  a  very  distinctly  reticular 
aspect,  and  being  in  part  beset  with  small  cells.  All  the  rest  of  the 
thickness  of  the  grey  matter  appears  mainly  to  contain  long  conical 
cells  (fig.  282,  5  ;  fig.  283,  3,  4),  the  distal  processes  or  apices  of  which 


•** 


FIG.  283. — SECTION  ACROSS  THE  HIPPOCAMPUS  MAJOR,  DENTATE  FISSURE,  DENTATE 

FASCIA  AND  FIMBRTA.      (Henle.) 

Gh,  part  of  the  gyrus  hippocampi  or  uncinate  convolution  ;  Fd,  fascia  dentata,  or  dentate 
convolution  ;  between  them  is  the  dentate  fissm-e  ;  Fi,  fimbria,  composed  of  longitudinal 
fibres  here  cut  across  ;  1,  2,  medullary  centre  of  the  hippocampal  gyrus  prolonged  around 
the  hippocampus,  //,  as  the  so-called  alveus,  into  the  fimbria ;  3,  layer  of  large  pyramidal 
cells ;  4,  their  processes  (stratum  radiatum)  ;  5,  reticular  neuroglia  (stratum  laciniosum)  ; 
6,  superficial  medullary  lamina,  involuted  around  the  dentate  fissure  ;  *  *,  termination  of 
this  lamina,  the  fibres  here  running  longitudinally ;  7,  superficial  neuroglia  of  the  fascia 
dentata ;  *,  ring  of  small  cells  within  this  (stratum  granulosum). 

are  prolonged  into  fibres  which  lose  themselves  in  the  superficial  layer 
of  neuroglia.  The  pyramidal  cells  rest  upon  the  white  centre,  here 
known  as  the  alveus  (1),  which  is  the  part  of  the  hippocampus  seen 


STRUCTURE  OF  THE  CEREBRUM. 


251 


within  the  ventricle,  and  which  is  prolonged  externally  into  the  fimbria 
(Fi),  where  its  fibres  become  longitudinal  in  direction. 

In  the  dentate  gyrus  (fascia  dentata,  fig.  283,  Fd)  the  pyramidal 
cells  are  arranged  in  an  irregularly  radiating  manner,  occupying  the 
centre  of  the  convolution,  and  surrounded  by  a  ring  of  closely  packed 
small  cells  (*).  External  to  these  is  a  thick  layer  of  superficial  neu- 
roglia  (7). 

The  olfactory  tract  is  an  outgrowth  of  the  brain  which  was  ori- 
ginally hollow,  and  remains  so  in  many  animals ;  but  in  man  the 
cavity  has  become  obliterated,  and  the  centre  is  occupied  by  neuroglia, 
containing  no  nerve-cells.  Outside  the  central  neuroglia  lies  the  white 


FIG.  284.  —SECTION  ACROSS  A  PART  OF  THE  OLFACTORY  BULB.     (Henle.) 

1,  3,  bundles  of  very  fine  transversely  cut  nerve-fibres,  forming  the  flattened  medullai-y  ring, 
enclosing  the  central  neuroglia  2  :  this  is  the  anterior  continuation  of  the  olfactory  tract ; 
5,  white  layer  with  numerous  small  cells  (granules) ;  (i,  mitral  layer  ;  7,  layer  of  olfactory 
glomeruli,  t,  tt  ;  8,  layer  of  olfactory  nerve-fibres,  bundles  of  which  are  seen  at  * 
passing  through  the  cribriform  plate  of  the  ethmoid  bone. 

or  medullary  substance,   consisting  of  bundles  of  longitudinal  white 
fibres.     Most  externally  is  a  thin  superficial  layer  of  neuroglia. 

The  olfactory  bulb  (fig.    284)  has  a  more  complicated    structure. 
Dorsally  there  is  a  flattened  ring  of  longitudinal  white  bundles  inclos- 


THE  ESSENTIALS  OF  HISTOLOGY. 

ing  neuroglia  (1,  2,  3),  as  in  the  olfactory  tract,  but  below  this  ring- 
several  layers  are  recognised  as  follows  : — 

1.  A  white  or  medullary  layer  (fig.  284,   4,  5),  characterised  by  the 
presence  of  a  large  number  of  small  cells  ("granules  ")  with  reticulating 
bundles    of  medullated    nerve-fibres    running   longitudinally   between 
them. 

2.  A  layer  of  large  nerve-cells  (6),  with  smaller  ones  intermingled,  the 
whole  embedded  in  an  interlacement  of  fibrils  which  are  mostly  derived 
from  the  cell-dendrites.     From  the  shape  of  most  of  the  large  cells  of 
this  layer  (fig.  285,  m.c.)  it  has  been  termed  the  "  mitral "  layer.     These 


olf.c. 


FIG.  285,— DIAGRAM  TO  SHOW  THE  RELATIONS  OF  CELLS  AND  FIBRES  IN  THE 
OLFACTORY  BULB. 

olf.c.,  olfactory  cells  of  M.  Schultze  in  the  olfactory  mucous  membrane,  sending  their 
basal  processes  as  iion-medullated  nerve-fibres  into  the  deepest  layer  of  the  olfactory 
bulb(o//.n.)  ;  gl,  olfactory  glomeruli  containing  the  terminal  arborisations  of  the  olfactory 
fibres  and  of  processes  from  the  mitral  cells ;  m,  mitral  cells,  sending  processes  down  to 
the  olfactory  glomeruli,  others  laterally  to  end  in  free  ramification  in  the  nerve-cell  layer, 
and  their  axis-cylinder  processes,  a,  a,  upwards,  to  turn  sharply  backwards  and  become 
fibres  of  the  olfactory  tract  (tr.olf.).  Numerous  collaterals  are  seen  curving  off  from  these 
fibres  :  «'.  a  nerve-fibre  of  the  olfactory  tract  apparently  ending  in  a  free  ramification  in 
the  olfactory  bulb. 

cells  send  their  axis-cylinder  processes  upwards  into  the  next  layer, 
and  they  eventually  become  fibres  jof  the  olfactory  tract  and  pass  along 
this  to  the  base  of  the  brain,  giving  off  numerous  collaterals  into  the 
bulb  as  they  pass  backwards  (v.  Gehuchten). 

3.  The  layer  of  olfactory  glomeruli  (fig.  284,  7  ;  fig.  285,  gl.)  consists  of 
rounded   nest-like  interlacements  of  fibrils  which  are  derived  on  the 


STRUCTURE  OF  THE  OLFACTORY  TRACT  AND  BULB.     253 

one  hand  from  the  terminal  arborisations  of  the  non-medullated  fibres 
which  form  the  subjacent  layer,  and  on  the  other  hand  from  arborisa- 
tions of  descending  processes  of  the  large  "  mitral "  cells  of  the  layer 
above. 

4.  This  is  the  layer  of  olfactory  nerve-fibres  (fig.  284,  8),  which  are  all 
non-medullated,  and  are  continued  from  the  olfactory  fibres  of  the 
Scheiderian  or  olfactory  mucous  membrane  of  the  nasal  fossae.  In 
this  mucous  membrane  they  take  origin  from  the  bipolar  olfactory 
cells  which  are  characteristic  of  the  membrane  (see  Lesson  XLIV.,  fig. 
309),  and  they  end  in  arborisations  within  the  olfactory  glomeruli, 
where  they  come  in  contact  with  the  arborisations  of  the  mitral  cells. 
The  relations  of  the  olfactory  cells  and  fibres  to  the  mitral  cells  and 
the  continuation  of  the  axis-cylinders  of  the  latter  upwards  and  back- 
wards to  join  the  optic  tract  are  shown  in  the  accompanying  diagram 
(fig.  285).  These  relations  have  only  recently  been  elucidated  by  the 
employment  of  the  method  of  Golgi  (see  Appendix),  chiefly  by  the 
researches  of  Golgi  himself  and  of  R.  y  Cajal. 

Basal  ganglia. — Besides  the  grey  matter  of  the  cerebral  cortex  the 
cerebral  hemispheres  conceal  in  their  deeper  parts  certain  other  masses 
of  grey  substance  (figs.  286,  287).  The  principal  of  these  are  the 
corpus,  striatum  (nucleus  caudatus,  n.c.  and  nucleus  lenticularis,  n.l.)  and 
optic  thalamus  (th.).  Between  them  run  the  bundles  of  white  fibres 
which  are  passing  upwards  from  the  cms  cerebri,  forming  a  white 
lamina  termed  the  internal  capsule.  Above  the  level  of  these  nuclei  the 
internal  capsule  expands  into  the  medullary  centre  of  the  hemisphere. 

The  nucleus  caudatus  of  the  corpus  striatum  is  composed  of  a 
reddish-grey  neuroglia  containing  both  moderately  large  and  small 
multipolar  nerve-cells.  It  receives  fibres  from  the  part  of  the  internal 
capsule  which  separates  it  from  the  nucleus  lenticularis,  and  next  to  the 
lateral  ventricle  it  is  covered  by  a  thin  layer  of  neuroglia  (ependyma), 
and  over  this  by  the  epithelium  of  the  cavity. 

The  nucleus  lenticularis,  which  corresponds  in  position  internally 
with  the  island  of  Reil  externally,  is  divided  by  two  white  laminas  into 
three  zones.  It  is  separated  from  the  nucleus  caudatus  and  optic 
thalamus  by  the  internal  capsule  (figs.  286,  287,  i.e.),  which  consists  of 
the  bundles  of  medullary  fibres  which  are  passing  between  the  white 
centre  of  the  hemisphere  and  the  crus  cerebri ;  it  receives  on  its  inner 
side  many  white  fibres  from  the  capsule,  and  these  impart  to  it  a 
radially  striated  aspect.  Many  of  the  nerve-cells  of  the  nucleus  lenti- 
cularis contain  yellow  pigment. 

The  optic  thalamus,  which  lies  at  the  side  of  the  third  ventricle 
and  forms  part  of  the  floor  of  the  lateral  ventricle,  is  covered  externally 


254  THE  ESSENTIALS  OF  HISTOLOGY. 

by  a  layer  of  white  fibres,  most  marked  next  to  the  internal  capsule, 
fibres  from  which  pass  into  the  thalamus  and  serve  to  connect  it  with 
the  hemisphere. 

The  grey  matter  of  the  thalamus  (fig.  286)  is  partially  subdivided  by 
an  oblique  white  lamina  into  a  smaller,  inner  (i),  and  a  larger,  outer, 
nucleus  (e) ;  these  contain  a  number  of  small  scattered  nerve-cells. 
Anteriorly  another  portion  of  grey  matter  (a)  is  divided  off  in  a  similar 
way  ;  this  contains  comparatively  large  nerve-cells. 

Attached  to  the  optic  thalamus  below  and  externally  are  the  two 
geniculate  bodies  which  are  connected  with  the  optic  tract.  Of  the  two 
geniculate  bodies  the  outer  has  a  lamellated  structure  consisting  of 
alternating  layers  of  grey  and  white  matter.  This  external  geniculate 
body  also  has  a  much  closer  connection  with  the  optic  tract  than  the 
inner ;  indeed,  it  is  doubtful  whether  the  latter  receives  any  fibres  from 
the  tract. 

The  tegmentum  of  the  crus  cerebri  is  prolonged  below  the  thala- 
mus opticus  into  a  mass  of  grey  substance,  with  longitudinally  and 
obliquely  crossing  white  bundles,  which  is  known  under  the  name  of 
subthalamic  substance.  In  it  at  least  three  parts  differing  from  one 
another  in  structure  may  be  distinguished  (see  fig.  286,  1,  2,  3). 

The  pineal  gland,  which  is  developed  in  the  roof  of  the  third 
ventricle,  is  composed  of  a  number  of  tubes  and  saccules  lined  and 
sometimes  almost  filled  with  epithelium,  and  containing  deposits  of 
earthy  salts  (brain-sand).  These  deposits  may,  however,  occur  in  other 
parts  of  the  brain.  The  follicles  are  separated  from  one  another  by 
vascular  connective-tissue  derived  from  the  pia  mater.1 

The  pituitary  body  is  a  small  reddish  mass  which  lies  in  the  sella 
turcica,  and  is  connected  with  the  third  ventricle  by  the  infundibulum. 
It  consists  of  two  lobes,  a  larger  anterior,  and  a  smaller  posterior. 
The  anterior  lobe  is  originally  developed  as  a  hollow  protrusion  of  the 
buccal  epithelium.  It  consists  of  a  number  of  tubules,  which  are  lined 
by  epithelium,  and  united  by  connective  tissue.  In  some  of  the  tubes 
the  epithelium  is  ciliated,  and  sometimes  a  colloid  substance  like  that 
occurring  in  the  vesicles  of  the  thyroid  has  been  found  in  them. 

The  posterior  lobe  of  the  pituitary  body,  although  developed  from  the 
floor  of  the  third  ventricle,  contains  scarcely  any  perceptible  nervous 
elements  in  the  adult.  It  consists  chiefly  of  vascular  connective  tissue. 

The  membranes  of  the  brain  are  similar  in  general  structure  to  those 
of  the  spinal  cord,  p.  216.  The  dura  mater  is,  however,  more  closely 

1  In  the  chameleon  and  some  other  reptiles,  the  pineal  is  better  developed,  and 
is  connected  by  nerve-fibres  with  a  rudimentary  median  eye  of  invertebrate  type, 
placed  upon  the  upper  surface  of  the  head. 


STRUCTURE  OF  THE  CORPUS  STRIATUM. 


255 


FIG.  28(>. -SECTION  ACROSS  THE  OPTIC  THALAMUS  AND  CORPUS  STRIATUM  IN  THE 

REGION  OF  THE   MIDDLE  COMMISSURE.      (Natural  size. ) 

dh.,  thalmus  ;  a,  e,  i,  its  anterior,  external,  and  internal  nuclei  respectively  ;  w,  its  external 
white  layer ;  m.c.,  middle  commissure  ;  v.  3,  third  ventricle  ;  a  small  part  is  also  seen 
below  the  middle  commissure;  c.c.,  corpus  callosum ;  /,  fornix,  separated  from  the 
third  ventricle  and  thalamus  by  the  velum  interpositum.  In  the  middle  of  this  are 
seen  the  two  veins  of  Galen  and  the  choroid  plexuses  of  the  third  ventricle  ;  and  at  its 
edges  the  choroid  plexuses  of  the  lateral  ventricles,  v.l.  ;  t.s.,  stria  pinealis ;  cr., 
forward  prolongation  of  the  crusta  passing  laterally  into  the  internal  capsule,  i.e. ; 
s.t.r.,  subthalamic  prolongation  of  the  tegmentum,  consisting  of  (1)  the  dorsal  layer, 
(2)  the  zona  incerta,  and  (3)  the  corpus  subthalamicum ;  s.n.,  substantia  nigra ;  n.c., 
nucleus  caudatu s  of  the  corpus  striatum ;  n.I..,  nucleus  lenticularis  ;  e.c.,  external  cap- 
sule ;  cl.,  claustrum  ;  7,  island  of  Reil;  h,  hippocampus;  d,  fascia  dentata. 


FIG.  287.  —  HORIZONTAL 
SECTION  THROUGH  THE 
OPTIC  THALAMUS  AND 
CORPUS  STRIATUM.  (Na- 
tural size. ) 

;\  I. ,  lateral  ventricle,  anterior 
cornu ;  e.c.,  corpus  callo- 
sum; s.l.,  septum  luci- 
dum  ;  a.f. ,  anterior  pillars 
of  the  fornix ;  v.  3,  third 
ventricle;  th.,  thalamus 
opticus  ;  s.  t. ,  stria  pine- 
alis ;  n.c.  ,iiucleus caudatus, 
and  n.I.,  nucleus  lenticul- 
aris of  the  corpus  stria- 
tum ;  i.e.,  internal  capsule  ; 
g.,  its  angle  or  genu  ;  n.c., 
tail  of  the  nucleus  caudatus 
appearing  in  the  descend- 
ing cornu  of  the  lateral 
ventricle  ;  cl,  claustrum  ; 
/,  island  of  Reil. 


256  THE  ESSENTIALS  OF  HISTOLOGY. 

adherent  to  the  under  surface  of  the  bony  cavity  than  is  the  case  in 
the  vertebral  canal.  The  arachnoid  is  in  many  places  close  to  the  dura 
mater,  and  separated  by  a  wide  subarachnoid  space,  which  is  bridged 
across  by  finely  reticulating  bands  of  areolar  tissue  (subarachnoid 
trabeculae)  from  the  pia  mater.  In  the  vicinity  of  the  longitudinal 
sinus,  small  rounded  elevations  (arachnoidal  villi,  Pacchionian  glands) 
project  into  the  dura  mater,  and  even  become  embedded  in  the  skull 
itself.  The  pia  mater  is  closely  adherent  to  the  surface  of  the  brain, 
and  dips  into  all  the  sulci,  but  without  forming  actual  folds  (Tuke). 
Jn  it  the  blood-vessels  ramify  before  passing  into  the  substance  of  the 
brain,  and  they  are  accompanied,  as  they  thus  enter  the  cerebral  sub- 
stance, by  prolongations  of  the  pia  mater,  which  do  not,  however, 
closely  invest  them,  but  leave  a  clear  space  around  each  vessel,  presum- 
ably for  the  passage  of  lymph  (perivascular  space).  The  capillary  net- 
work is  much  closer  in  the  grey  than  in  the  white  matter. 


STRUCTURE  OF  THE  EYELIDS.  257 


LESSONS  XLIL  AND  XLIIL 

STRUCTURE  OF  THE  EYELIDS  AND   OF  THE  PARTS  OF 
THE  EYEBALL. 

LESSON  XLII. 

1.  SECTIONS  of  the  eyelid  vertical  to  its  surfaces  and  transverse  to  its  long 
axis.  The  lid  should  be  hardened  in  alcohol,  and  the  sections  may  be  stained 
with  haematoxylin  and  mounted  in  the  usual  manner  in  Canada  balsam. 

Notice  the  long  sacculated  Meibomian  glands  lying  in  dense  connective 
tissue  close  to  the  conjunctival  surface,  and  their  ducts  opening  at  the 
margin  of  the  lid.  External  to  these  the  small  fibres  of  the  orbicularis  pal- 
pebrarum  cut  across  ;  a  few  of  the  fibres  of  the  muscle  lie  on  the  conjunctival 
side  of  the  duct.  A  short  distance  from  the  Meibomian  gland  may  be 
observed  another  tolerably  large  sebaceous  gland  ;  outside  this  again  are  the 
eyelashes.  In  the  skin  covering  the  outer  surface  of  the  eyelid  a  few  small 
hairs  may  be  seen.  At  the  attached  part  of  the  eyelid  are  some  bundles  of 
involuntary  muscular  fibres  cut  longitudinally  in  the  section,  and  in  the  upper 
eyelid  the  fibrous  attachment  of  the  elevator  muscle  may  be  observed  attached 
to  the  dense  connective  tissue. 

Make  a  general  sketch  under  a  low  power. 

2.  Sections  through  the  posterior  part  of  an  eyeball  that  has  been  hardened 
in  Mliller's  fluid.     The  sections  are  stained  and  mounted  in  the  usual  way. 
These  sections  will  show  the  relative  thickness  of  the  several  coats  and  the 
layers  of  which  each  coat  is  formed.      Sections  which  pass  through  the  point 
of  entrance  of  the  optic  nerve  will  also  exhibit  the  manner  in  which  the 
nerve-fibres  pierce  the  several  coats  to  reach  the  inner  surface  of  the  retina. 
The  modifications  which  are  found  in  the  neighbourhood  of  the  yellow  spot 
may  also  be  made  out  if  the  sections  have  been  taken  from  the  human  eye. 

3.  Sections  of  the  anterior  half  of  an  eyeball  which  has  been  hardened  in 
Miiller's  fluid.     These  sections  should  pass  through  the  middle  of  the  cornea. 
The  lens  may  be  left  in  situ,  but  this  renders  the  preparation  of  the  sections 
and  the  mounting  of  them  much  more  difficult  on  account  of  the  extreme 
hardness  which  is  imparted  to  the  lens-tissue  by  alcohol.1 

In  these  sections  make  a  general  sketch  under  a  low  power,  showing  the 
relations  of  the  several  parts  one  with  another ;  and  study  carefully,  and  sketch 
in  detail,  the  layers  of  the  cornea,  the  place  of  junction  of  the  cornea  and 
sclerotic,  the  ciliary  muscle,  the  muscular  tissue  of  the  iris,  the  mode  of  sus- 
pension of  the  lens,  and  the  pars  ciliaris  retinae. 

4.  Mount  in  glycerine  thin  tangential  sections  of  a  cornea  stained  with 
chloride  of  gold  by  Cohnheim's  method.     Sketch  three  or  four  of  the  con- 
nective-tissue cells  (corneal  corpuscles).     The  arrangement  and  distribution 

1  The  celloidin  method  of  embedding  is  well-adapted  for  preparations  of  this  kind  (see 
Appendix). 

R 


258  THE  ESSENTIALS  OF  HISTOLOGY. 

of  the  nerve-fibres  and  their  termination  amongst  the  epithelium-cells  as 
shown  in  chloride  of  gold  preparations  have  been  already  studied  (Lesson 
XXL). 

5.  Mount  in  Canada  balsam  sections  of  a  cornea  which  has  been  stained 
with  nitrate  of  silver.  Notice  the  branched  cell-spaces  corresponding  with 
the  connective-tissue  cells  of  the  last  preparation. 

[This  preparation  is  best  made  by  rubbing  the  surface  of  the  cornea  with 
lunar  caustic  after  scraping  off  the  epithelium.  After  ten  or  fifteen  minutes 
(by  which  time  the  nitrate  of  silver  will  have  penetrated  the  thickness  of  the 
cornea)  the  eye  is  washed  with  distilled  water,  and  exposed  to  the  light. 
When  brown,  tangential  sections  may  be  made,  for  which  purpose  the  cornea 
may  be  hardened  in  spirit.] 


LESSON  XLIII. 

].  REMOVE  the  sclerotic  from  the  anterior  part  of  an  eye  which  has  been 
preserved  in  Miiller's  fluid,  and  tear  off  thin  shreds  from  the  surface  of  the 
choroid,  including  amongst  them  portions  of  the  ciliary  muscle.  Stain  the 
shreds  with  hsematoxylin  and  mount  them  in  Farrant.  Sketch  the  branched 
pigment-cells,  the  elastic  network,  the  mode  of  attachment  of  the  fibres  of 
the  ciliary  muscle,  etc. 

2.  Injected  preparation  of  choroid  and  iris.     Mount  in  Canada  balsam  por- 
tions of  the  choroid  coat  and  iris  from  an  eye,  the  blood-vessels  of  which  have 
been  filled  with  coloured  injection.     Make  sketches  showing  the  arrangement 
of  the  capillaries  and  veins. 

3.  Teased  preparation  of  retina.      Break  up  with  needles  in  a  drop  of 
glycerine  a  minute  fragment  of  retina  which  has  been  placed  in  1  per  cent, 
osmic  acid  solution  for  a  few  hours,  and  has  subsequently  been  kept  in  dilute 
glycerine.     Complete  the  separation  of  the  retinal  elements  by  tapping  the 
cover-glass.      Draw   carefully   under   a   high   power   some   of    the   isolated 
elements — e.g.  the  rods  and  cones  with  their  attached  fibres  and  nuclei,  the 
inner  granules,  the  ganglion-cells,  the  fibres  of  Miiller,  hexagonal  pigment- 
cells,  etc.     In  some  of  the  fragments  the  arrangement  of  the  elements  in  the 
retinal  layers  may  be  made  out  even  better  than  in  actual  sections.1 

Measure  the  length  and  diameter  of  some  of  the  cones,  the  length  of  the 
cone-fibres,  and  the  diameter  of  some  of  the  outer  and  inner  nuclei. 

4.  Teased  preparation  of  lens.     Separate  in  water  the  fibres  of  a  crystalline 
lens  which  has  been  macerated  for  some  days  in  bichromate  of  potash  solu- 
tion.    Sketch  some  of  the  fibres,  together  and  separate. 


The  eyelids  (fig.  288)  are  covered  externally  by  the  skin,  and  inter- 
nally or  posteriorly  by  a  mucous  membrane,  the  conjunctiva,  which  is 
reflected  from  them  over  the  globe  of  the  eye.  They  are  composed  in 
the  main  of  connective  tissue,  which  is  dense  and  fibrous  under  the 
conjunctiva,  where  it  forms  what  is  known  as  the  tarsus. 

Embedded  in  the  tarsus  is  a  row  of  long  sebaceous  glands  (the 

1  The  distribution  of  the  nerve-fibres  and  cell-processes  within  the  retina  can  only  be 
made  out  satisfactorily  by  the  employment  of  Golgi's  method  (see  Appendix). 


STRUCTURE  OF  THE  EYELIDS. 


259 


Meibomian  glands,  /),  the  ducts  of  which  open  at  the  edge  of  the  eyelid. 
The  rest  of  the  thickness  of  the  eyelid  is  composed  of  a  somewhat  loose 
connective  tissue,  and  contains  the  bundles  of  the  orbidtla/ris  muscle  (b). 
In  the  upper  eyelid  the  levatar  palpebra?  is  inserted  into  the  tarsus  by  a 
fibrous  expansion,  and  some  bundles  of  involuntary  muscle  are  also 


FIG.  288.—  VBBTICAL  SECTION  THROUGH  THE  UPPER  EYELID.     (Waldeyer.) 
(Magnified.) 

a,,  skin  ;  b,  orbicularis  ;  b',  ciliary  bundle  ;  c,  involuntary  muscle  of  eyelid ;  d,  conjunctiva  ; 
e,  tarsus  with  Meibomian  gland  ;  /,  duct  of  the  gland  ;  g,  sebaceous  gland  near  eyelashes ; 
h,  eyelashes  ;  i,  small  hairs  in  outer  skin  ;  j,  sweat-glands ;  k,  posterior  tarsal  glands. 

present  near  the  attachment  of  the  eyelid.  The  skin  has  the  usual 
structure ;  it  contains  small  sweat-glands  and  the  follicles  of  small 
hairs,  and,  in  addition,  at  the  edge  of  the  eyelid,  the  large  hair-follicles 
from  which  the  eyelashes  grow.  The  epithelium  of  the  conjunctiva 


260 


THE  ESSENTIALS  OF  HISTOLOGY. 


palpebrse  is  columnar,  passing  at  the  edge  of  the  lid  into  the  stratified 
epithelium  of  the  skin ;  it  also  becomes  stratified  in  the  part  which  is 
reflected  over  the  globe  of  the  eye.  The  nerves  of  the  conjunctiva 


FIG.  289.— VERTICAL  SECTION  OF  HUMAN  CORNEA  FROM  NEAR  THE  MARGIN. 
(Waldeyer.)     (Magnified.) 

1,  epithelium  ;  2,  anterior  homogeneous  lamina  ;  3,  substantia  propria  comese  ;  4,  posterior 
homogeneous  (elastic)  lamina  ;  5,  epithelium  of  the  anterior  chamber  ;  a,  oblique  fibres 
in  the  anterior  layer  of  the  substantia  propria  ;  b,  lamellae,  the  fibres  of  which  are  cut 
across,  producing  a  dotted  appearance  ;  c,  corneal  corpuscles  appearing  fusiform  in  sec- 
tion ;  d,  lamellae  with  the  fibres  cut  longitudinally  ;  e,  transition  to  the  sclerotic,  with 
more  distinct  fibrillation,  and  surmounted  by  a  thicker  epithelium ;  /,  small  blood-vessels 
cut  across  near  the  margin  of  the  cornea. 

terminate  for  the  most  part  in  end-bulbs,  which  in  man  are  spheroidal, 
and  formed  chiefly  of  a  small  mass  of  polyhedral  cells,  but  in  the  calf 


STRUCTURE  OF  THE  COATS  OF  THE  EYEBALL.  261 

and  most  animals  they  are  elliptical,  and  consist  of  a  core  and  lamel- 
lated  sheath  (see  Lesson  XXL). 

The  lachrymal  gland  may  be  briefly  mentioned  in  connection  with 
the  eyelid.  It  is  a  compound  racemose  gland,  yielding  a  watery  secre- 
tion, and  resembling  in  structure  the  serous  salivary  glands,  such  as  the 
parotid.  Its  ducts,  of  which  there  are  several,  open  at  the  upper  fold 
of  the  conjunctiva,  near  its  outer  extremity. 

The  sclerotic  coat  is  composed  of  dense  fibrous  tissue,  the  bundles 
of  which  are  intimately  interlaced.  It  is  thickest  at  the  back  of  the 
eyeball.  It  is  covered  externally  with  a  lymphatic  epithelium,  while 
internally  it  is  lined  by  a  layer  of  connective  tissue  containing  pig- 
ment-cells, which  give  it  a  brown  appearance  (lamina  fusca).  At  the 
entrance  of  the  optic  nerve  the  sclerotic  is  prolonged  into  the  sheath 
of  that  nerve,  the  bundles  of  which,  piercing  the  coat,  give  a  sieve-like 
aspect  to  the  part  (lamina  cribrosa,  fig.  298,  L). 


FIG.  290.  —  A.  CORPUSCLES  OF  THE  RAT'S  CORNEA.  (From  a  preparation  treated 
with  chloride  of  gold.)  B.  CELL-SPACES  OF  THE  RAT'S  CORNEA.  (From  a 
preparation  stained  with  nitrate  of  silver.) 

The  cornea  (fig.  289)  consists  of  the  following  layers  enumerated 
from  before  back : — 

1.  A   stratified    epithelium   continuous  with   the   epithelium    of  the 
conjunctiva  (1). 

2.  A  thin  lamina  of  homogeneous  connective  tissue   (membrane  of 
Bowman),  upon  which  the  deepest  cells  of  the  epithelium  rest  (2). 

3.  A  thick  layer  of  fibrous  connective  tissue  which  forms  the  proper 
substance  of  the  cornea  (3).     This  is  continuous  laterally  with  the  tissue 
of  the  sclerotic.     It  is  composed  of  bundles  of  white  fibres  arranged  in 
regular  lamina?,  the  direction  of  the  fibres  crossing  one  another  at  right 


•26-2  THE  ESSENTIALS  OF  HISTOLOGY. 

angles  in  the  alternate  laminae.  Between  the  laminae  lie  flattened  con- 
nective-tissue corpuscles,  which  are  branched  and  united  by  their 
processes  into  a  continuous  network ;  there  is  of  course  a  corresponding 
network  of  cell-spaces  (fig.  290,  A,  B).  In  vertical  sections  the  cells 
appear  narrow  and  spindle-shaped  (fig.  289,  c).  In  the  superficial 
laminae  there  are  a  few  bundles  of  fibres  which  run  obliquely  towards 
the  surface  (a). 

4.  A  homogeneous  elastic  layer  (membrane  of  Descemet,  fig.  289,  4). 
This  completely  covers  the  back  of  the  cornea,  but  at  the  angle  which 
the  cornea  forms  with  the  iris  it  breaks  up  into  separate  fibres,  which 
are  continued  into  the  iris  as  the  ligamentum  pectinatutn,  or  pillars  of 
the  iris. 


FIG.  291.— SECTION  OF  CHOROID.    (Cadiat.) 

a,  membrane  of  Bvuch  :  the  chorio-capillaris  is  just  above  it;  b,  vascular  layer  ;  c,  vessels 
with  blood-corpuscles  ;  d,  lamina  suprachoroidea. 

5.  A  layer  of  pavement-epithelium  (endothelium  of  Descemet's  mem- 
brane) covering  the  posterior  surface  of  the  elastic  lamina,  and  lining 
the  front  of  the  anterior  chamber  of  the  eye  (fig.  289,  5).  At  the  sides 
it  is  continued  over  the  ligamentum  pectinatum  into  a  similar  endothe- 
lium, covering  the  anterior  surface  of  the  iris  (fig.  294).  The  cells  of 
the  epithelium  of  Descemet's  membrane  are  separated  from  one  another 
by  intercellular  spaces,  bridged  across  by  bundles  of  fibrils  which  pass 
through  the  cells. 

The  nerves  of  the  cornea  pass  in  from  the  periphery,  losing  their 
medullary  sheath  as  they  enter  the  corneal  substance.  They  form  a 
primary  plexus  in  the  substantia  propria,  a  secondary  or  sub-epithelial 
plexus  immediately  under  the  epithelium  which  covers  the  anterior- 
surface,  and  a  terminal  plexus  of  fine  fibrils  which  pass  from  the  sub- 
epithelial  plexus  in  pencil-like  tufts  and  become  lost  between  the  epi- 
thelium-cells (see  figs.  125,  126,  Lesson  XXL).  There  are  no  blood- 
vessels or  lymphatics  in  the  cornea,  although  they  come  close  up  to  its 
margin. 

The  choroid  or  vascular  coat  of  the  eye  is  of  a  black  colour  in  many 


STRUCTURE  OF  THE  CHOROID  COAT. 


263 


FIG.  292.— A  SMALL  PORTION  OF  THE  LAMINA  SUPRACHOBOIDEA.    (Highly  magnified.) 

p  pigment-cells ;  /,  elastic  fibres  ;  n,  nuclei  of  endothelial  cells  (the  outlines  of  the 
cells  are  not  indicated) ;  I,  lymph-cells. 


FIG.  293.— INJECTED  BLOOD-VESSELS  OF  THE  CHOROID  COAT.    (Sappey.) 

1,  one  of  the  larger  veins  ;  2,  small  anastomosing  vessels  ;  3,  branches 
dividing  into  the  smallest  vessels. 


264 


THE  ESSENTIALS  OF  HISTOLOGY. 


animals,  but  in  the  human  eye  it  is  dark  brown.  It  is  composed  of 
connective  tissue,  the  cells  of  which  are  large  and  filled  with  pigment 
(figs.  291,  292),  and  it  contains  in  its  inner  part  a  close  network  of 
blood-vessels,  and  in  its  anterior  part  the  involuntary  muscular  fibres 


FIG.  294.— SECTION   (FROM  THE  EYE  OF  A   MAN,    AGED  30),   SHOWING  THE 
RELATIONS   OF  THE  CORNEA,   SCLEROTIC,   AND  IRIS,  TOGETHER  WITH  THE 

CILIARY    MUSCLE,    AND    THE    CAVERNOUS    SPACES    NEAR   THE    ANGLE    OF    THE 

ANTERIOR  CHAMBER.     (Waldeyer. )    (Magnified.) 

A,  epithelium ;  B,  conjunctival  mucous  membrane ;  C,  sclerotic  ;  D,  membrana  supracho- 
roidea  ;  E,  opposite  the  ciliary  muscle  ;  F,  choroid,  with  ciliary  processes  ;  G,  tapetum 
nigrum  and  pars  ciliaris  retinae  ;  //,  cornea  (substantia  propria) ;  /,  iris  ;  K,  radiating 
and  meridional,  and  L,  circular  or  annular  bundles  of  the  ciliary  muscle ;  M,  bundles 
passing  to  the  sclerotic  ;  N,  ligamentum  pectinatum  iridis  at  the  angle,  0,  of  the  an- 
terior chamber  ;  P,  line  of  attachment  of  the  iris.  1,  anterior  homogeneous  lamina  of 
the  cornea  ;  2,  posterior  homogeneous  lamina,  covered  with  endothelial  cells  which  are 
continued  over  the  front  of  the  iris ;  3,  cavernous  spaces  at  the  angle  of  the  anterior 
chamber  (spaces  of  Fontana) ;  4,  canal  of  Schlemm,  with  endothelial  lining,  and  with  a 
vessel,  5,  leading  from  it ;  6,  other  vessels  ;  7,  bundles  of  fibres  of  the  sclerotic  having 
a  circular  direction,  cut  across  ;  8,  larger  ones  in  the  substance  of  the  sclerotic  ;  0,  fine 
bundles  cut  across,  at  limit  of  cornea ;  10,  point  of  origin  of  meridional  bundles  of 
ciliary  muscle  ;  11,  blood-vessels  in  sclerotic  and  conjunctiva,  cut  across ;  12,  section 
of  one  of  the  ciliary  arteries. 

of  the  ciliary  muscle,  which  pass  backwards  from  their  origin  at  the 
junction  of  the  cornea  and  sclerotic,  to  be  inserted  into  the  choroid. 
The  choroid  is  separable  into  the  following  layers,  enumerated  from 
without  in : — 


STRUCTURE  OF  THE  CHOROID  COAT. 


265 


1.  The  lamina  suprachoroidea  (fig.  291,  d).     This  is  a  thin  membrane 
composed  of  homogeneous  connective  tissue  pervaded  by  a  network  of 
fine  elastic  fibres,   and  containing  many  large  branched  pigment- cells 
and  lymph-corpuscles  (fig.  292).     It  is  covered  superficially  by  a  delicate 
lymphatic  endothelium,  and  is  separated  from  the  lamina  fusca  by  a  cleft- 
like  lymphatic  space  which  is  bridged  across  here  and  there  by  the 
passage  of  vessels  and  nerves,  and  by  bands  of  connective  tissue. 

2.  The  vascular  layer  of  the  choroid  (fig.  291,  b),  which  resembles 
the  suprachoroidea  in  structure,  but  contains  the  blood-vessels  of  the 
coat.     In  its  outer  part  are  the  larger  vessels  (arteries  and  veins),  the 
veins   having  a   peculiar   vorticose    arrangement ;    in   its   inner   part 


FIG.  295.— SEGMENT  OF  THE  IRIS,  SEEN  FROM  THE  POS- 
TERIOR   SURFACE     AFTER     REMOVAL    OF    THE     UVEAL 
PIGMENT.      (Iwanoff.) 
a,  sphincter  muscle  ;  b,  dilatator  muscle  of  the  pupil. 


FIG.  296.— VESSELS  OF  THE  CHOROID,  CILIARY  PROCESSES 
AND  IRIS  OF  A  CHILD.     (Arnold.)     (10  diameters.) 

•a,  capillary  network  of  the  posterior  part  of  the  choroid,  ending 
at  b,  the  ora  serrata  ;  c,  arteries  of  the  corona  ciliaris,  supplying 
the  ciliary  processes,  d,  and  passing  into  the  iris,  e  ;  /,  the  ca- 
pillary network  close  to  the  pupillary  margin  of  the  iris. 

(chorio-capillaris)  are  the  capillaries,  which  form  an  extremely  close 
network  with  elongated  meshes,  the  capillaries  radiating  from  the 
extremities  of  the  small  arteries  and  veins  in  a  highly  characteristic 
manner  (fig.  293).  In  the  ciliary  processes  the  vessels  have  for  the 
most  part  a  longitudinal  direction,  but  there  are  numerous  convoluted 
transversely  disposed  capillaries  uniting  the  longitudinal  vessels  (fig.  296). 

3.  Lining  the  inner  surface  of  the  choroid  is  a  very  thin  transparent 
membrane  known  as  the  membrane  of  Bruch  (fig.  291,  a), 

The  ciliary  muscle  of  Bowman  consists  of  involuntary  muscular  bundles 
which  arise  at  the  corneo-sclerotic  junction,  and  pass  meridionally  back- 
wards to  be  inserted  into  the  choroid  (fig.  294,  K).  Many  of  the 
deeper-seated  bundles  take  an  oblique  direction,  and  these  pass  gradu- 


266 


THE  ESSENTIALS  OF  HISTOLOGY. 


ally  into  others  which  run  circularly  around  the  circumference  of  the 
iris,  and  on  a  level  with  the  ciliary  processes.  This  set  of  circularly 
arranged  bundles  constitutes  the  circular  ciliary  muscle  of  H.  Muller  (L) ; 
it  is  most  marked  in  hypermetropic  eyes. 

The  iris  is  that  part  of  the  vascular  coat  of  the  eye  which  extends  in 
front  of  the  lens.     It  is  continuous  with  the  choroid  and  has  a  similar 


Outer  or  choroidal  surface. 


8.  Layer  of  pigment-cells. 


7.  Layer  of  rods  and  cones. 


.     .  Membrana  limitans  externa. 


(5.  Outer  nuclear  layer. 


5.  Outer  moleciilar  layer. 


4.  Inner  nuclear  layer. 


3.  Inner  molecular  layer. 


2.  Layer  of  nerve-cells. 
1.  Layer  of  nerve-fibres. 

.     .     .  Membrana  limitans  interna. 

Inner  surface. 

FIG.  297.— DIAGRAMMATIC  SECTION  OF  THE  HUMAN  RETINA.     (M.  Schultze.) 

structure,  but  its  pigment-cells  often  contain  variously  coloured  pig- 
ment. Besides  the  homogeneous  connective  tissue  with  numerous 
elastic  fibres  and  blood-vessels  of  which  it  is  chiefly  composed,  it  con- 
tains two  sets  of  plain  muscular  fibres.  The  one  set  forms  the  sphincter 
muscle  (fig.  295,  a),  which  encircles  the  pupil,  the  other  set  consists  of 
a  flattened  layer  of  radiating  fibres  which  extend  from  the  attachment 


STRUCTURE  OF  THE  IRIS. 


267 


of  the  iris  nearly  to  the  pupil,  lying  close  to  the  posterior  surface  and 
constituting  the  dilatator  muscle  (b).1 

The  back  of  the  iris  is  covered  by  a  thick  layer  of  pigraented 
epithelium  (uvea)  continuous  with  the  epithelium  of  the  pars  ciliaris 
retinae. 

The  blood-vessels  of  the  iris  converge  towards  the  pupil  (fig.  296,  e). 
Near  the  pupil  the  small  arteries  form  a  small  anastomotic  circle,  from 
which  capillaries  arise  and  pass  still  nearer  the  pupil,  around  which 
they  form  a  close  capillary  network. 


FIG.  298.— SECTION  THROUGH  THE  COATS  OF  THE  EYEBALL  AT  THE  POINT  OF 

ENTRANCE  OF  THE  OPTIC  NERVE.   (Toldt.) 

Ve,  dural  sheath ;  Vm,  arachnoidal  sheath,  and  Vi,  pia-niatral  sheath  of  the  optic  nerve, 
with  lymphatic  spaces  between  them  ;  0,  0,  funiculi  of  the  nerve  ;  L,  lamina  cribrosa  ; 
A,  central  artery ;  S,  sclerotic ;  Ch,  choroid  ;  R,  retina.  The  small  letters  refer  to  the 
various  parts  of  the  retina,  b  being  the  layer  of  rods  and  cones,  and  i  that  of  nerve-fibres. 

A  large  number  of  nerve-fibres  are  distributed  to  the  choroid  and 
iris,  probably  going  chiefly  to  the  muscular  tissue  (ciliary  muscle  and 
sphincter  and  dilatator  iriclis). 

The  retina  consists  of  the  eight  layers  shown  in  the  accompanying 
figure  (fig.  297),  numbered  as  they  occur  from  within  out. 

The  inner  surface  of  the  retina,  which  is  smooth,  rests  upon  the 
hyaloid  membrane  of  the  vitreous  humour.  It  is  formed  of  the  united 
bases  of  the  fibres  of  Miiller,  which  will  be  afterwards  described. 

The  layer  of  nerve-fibres  is  formed  by  the  expansion  of  the  optic  nerve 
after  it  has  passed  through  the  coats  of  the  eye  (fig.  298).  At  its  en- 

1  The  existence  of  a  dilatator  is  denied  by  some  histologists. 


268  THE  ESSENTIALS  OF  HISTOLOGY. 

trance  it  forms  a  slight  eminence  (colliculus  nervi  optici).  The  nerve- 
fibres  lose  their  medullary  sheath  on  reaching  the  retina.  Some  of 
the  fibres  pass  through  the  ganglionic  and  molecular  layers  to  form  a 
terminal  arborisation  in  the  inner  nuclear  layer  (fig.  299).  The  layer 
of  nerve-fibres  becomes  gradually  thinner  in  the  anterior  part  of  the 
retina. 

The  layer  of  nerve-cells,  or  ganglionic  layer,  is  composed  of  nerve-cells 
somewhat  like  the  cells  of  Purkinje  of  the  cerebellum  but  varying  in 
size,  although  those  of  large  size  are  prevalent  in  most  parts  of  the 
retina.  On  the  other  hand,  in  the  yellow  spot  small  bipolar  nerve-cells 
are  met  with,  and  they  may  here  lie  several  deep.  These  nerve-cells 
have  on  the  one  side  a  fine  axis-cylinder  process  prolonged  into  a  fibre 
of  the  layer  just  noticed,  and  on  the  other  a  thick  branching  process,  the 
ramifications  of  which  terminate  in  the  next  layer  in  flattened  arborisa- 
tions at  different  levels  (fig.  300,  A,  B,  C). 

The  inner  molecular  layer  is  comparatively  thick,  and  has  an  appear- 
ance very  like  the  grey  matter  of  the  nerve-centres.  A  few  nuclei  are 
scattered  through  it,  and  it  is  traversed  by  the  processes  of  the  nerve- 
cells  and  of  the  inner  granules,  and  by  fibres  from  the  optic  nerve  layer 
as  well  as  by  the  fibres  of  Miiller. 

The  inner  nuclear  layer  is  mainly  composed  of  bipolar  nerve-cells  con- 
taining large  nuclei  (inner  granules).  The  processes  of  these  cells  (fig. 
301,  D)  extend  on  the  one  hand  inwards  into  the  inner  molecular  layer 
where  they  spread  out  into  terminal  arborisations  at  different  levels, 
whilst  the  other  process  is  directed  outwards,  and,  after  forming  an 
arborisation  in  the  outer  molecular  layer,  is  continued  on  as  far  as  the 
external  limiting  membrane,  where  it  appears  to  end  in  a  free  pointed 
extremity  (E).  Besides  these  bipolar  nerve-cells,  there  are  other  inner 
granules  which  are  different  in  character,  having  ramified  processes 
which  only  extend  into  one  or  other  of  the  molecular  layers,  in  which 
the  bodies  of  these  cells  are  often  partly  embedded.  The  cells  in  ques- 
tion are  partly  of  the  nature  of  neuroglia-cells  (fig.  301,  C  and  H),  but 
others  (A,  B,  I)  may  perhaps  be  regarded  as  nerve-cells,  since  they  have 
been  noticed  to  give  off,  besides  branching  processes  or  dendrites,  which 
ramify  in  the  molecular  layer,  an  axis-cylinder  process  which  may 
extend  into  the  nerve-fibre  layer.  The  fibres  of  Miiller  have  nucleated 
enlargements  (J)  in  the  inner  nuclear  layer. 

The  outer  molecular  layer  is  thin,  and  is  composed  mainly  of  the  arborisa- 
tions of  the  inner  granules  and  of  the  rod-and-cone  fibres  (fig.  301,  5). 

As  far  as  the  outer  molecular  layer  the  retina  may  be  said  to  consist 
of  nervous  elements,  but  beyond  this  layer  it  is  formed  of  modified 
epithelium-cells. 


STRUCTURE  OF  THE  RETINA. 


FIG.  299.— SECTION  THROUGH  THE  INNER  LAYERS  OF  RETINA  OF  A  BIRD,  PREPARED- 

BY  GOLGI'S  METHOD.     (R.  y  Cajal.) 

A,  nerve-fibres  of  optic  nerve  layer;  B,  some  of  these  fibres  passing  through  the  inner 
molecular  layer  to  end  in  an  arborisation  at  the  junction  of  the  inner  molecular  and 
inner  nuclear  layers.  The  layers  in  this  and  in  the  two  succeeding  cuts  are  numbered 
in  correspondence  with  the  layers  in  fig.  2(,»7. 


FIG.  300. — SECTION  ACROSS  THE  MOLECULAR  AND  GANGLIONIC  LAYERS  OF  BIRD'S 

RETINA,    PREPARED  BY   GOLGl'S    METHOD.      (R.  y  Cajal.) 

Three  or  four  ganglionic  cells,  A,  B,  C,  and  the  terminal  arborisations  of  their  dendrites, 
a,  6,  c,  in  the  molecular  layer,  are  shown. 


FIG.  301.— SECTION  OF  BIRD'S  RETINA,  PREPARED  BY  GOLGI'S  METHOD.  (R.  y  Cajal.) 
A,  B,  large  nerve-cells  of  inner  nuclear  layer ;  C,  neuroglia-cell ;  D,  small  bipolar  nerve-cells 
with  one  process,  a,  b,  ramifying  in  the  inner  molecular  layer  and  the  other  one  ramifying 
in  the  outer  molecular  layer,  and  extending  (E)  as  far  as  the  rods  and  cones  ;  F,  G,  rod  and 
cone  nuclei  respectively;  H,  I,  cells  with  dendrites  ramifying  in  outer  molecular  layer- 
J,  fibre  of  Mtiller. 


270 


THE  ESSENTIALS  OF  HISTOLOGY. 


The  outer  nuclear  layer  and  the  layer  of  rods  and  cones  are  composed  of 
elements  which  are  continuous  through  the  two  layers,  and  they  should 
properly,  therefore,  be  described  as  one.  It  may  be  termed  the  sensory 
or  nerve-epithelium  of  the  retina  (fig.  302,  6  and  7).  The  elements  of 
which  this  nerve-epithelium  consists  are  elongated,  nucleated  cells  of 
two  kinds.  The  most  numerous,  which  we  may  term  the  rod-elements, 
consist  of  peculiar  rod-like  structures  (rods  proper)  set  closely  side  by 
side,  and  each  of  which  is  prolonged  internally  into  a  fine  varicose  fibre 
(rod-fibre]  which  swells  out  at  one  part  of  its  course  into  a  nucleated 
enlargement,  and  ultimately  ends  in  an  arborisation  within  the  outer 


FIG.  302. — DIAGRAMMATIC  REPRESENTATION  OF  SOME  OF  THE  NERVOUS  AND 

EPITHELIAL  ELEMENTS  OF  THE   RETINA.      (After  Schwalbe.) 
The  designation  of  the  numbers  is  the  same  as  in  fig.  297. 

molecular  layer.  The  rod  proper  consists  of  two  segments,  an  outer 
cylindrical  and  transversely  striated  segment,  which  during  life  has  a 
purplish-red  colour,  and  an  inner  slightly  bulged  segment,  which  in 
part  of  its  length  is  longitudinally  striated.  The  nucleus  of  the  rod- 
element  often  has,  in  the  fresh  condition,  a  transversely  shaded  aspect 
{fig.  302).  The  cone-elements  are  formed  of  a  conical  tapering  external 


STRUCTURE  OF  THE  RETINA. 


271 


part,  the  cone  proper,  which  is  directly  prolonged  into  a  nucleated 
enlargement,  from  the  farther  side  of  which  the  cone-fibre,  considerably 
thicker  than  the  rod-fibres,  passes  inwards,  to  terminate  by  an  ex- 
panded arborisation  in  the  outer  molecular  layer.  The  cone  proper, 
like  the  rod,  is  formed  of  two  segments,  the  outer  of  which,  much  the 
smaller,  is  transversely  striated,  the  inner,  bulged  segment  being  longi- 
tudinally striated.  The  inner  ramified  ends  of  the  rod-and-cone  fibres 
are  believed  to  come  in  contact  with  the  arborisations  of  the  inner 


m.e.l. 


FlG.     303. — PlGMENTED     EPITHELIUM      OF 
THE     HUMAN     KETINA.        (M.    Schultze.) 

(Highly  magnified.) 

a,  cells  seen  from  the  outer  surface  with  clear 
lines  of  intercellular  substance  between  ;  6, 
two  cells  seen  in  profile  with  fine  offsets  ex- 
tending inwards  ;  c,  a  cell  still  in  connection 
with  the  outer  ends  of  the  rods. 


FlG.    304.— A  FIBRE   OF  MtJLLER  FROM   THE 
HUMAN   RETINA,    ISOLATED.     (Henle.)    J--0T°A 

b,  base  of  the  fibre  ;  n,  its  nucleus  ;  m.e.l.,  mem- 
brana  limitans  externa  ;  e.m.l.,  external  mo- 
lecular layer. 


t.in.  I. 


granules,  and  through  these  elements  and  their  arborisations  in  the 
inner  molecular  layer  a  connection  is  probably  brought  about  with  the 
ganglionic-cells  and  nerve-fibres  of  the  innermost  layers.  There 
appears,  however,  to  be  no  anatomical  continuity  between  the  several 


272 


THE  ESSENTIALS  OF  HISTOLOGY. 


elements,  but  merely  an  interlacement  of  ramified  fibrils  (fig.  301).  In 
birds,  reptiles,  and  amphibia,  a  small  oil-globule,  often  brightly  coloured 
red,  yellow,  or  green,  is  found  in  the  inner  segment  of  each  cone,  and  other 
variations  of  structure  are  met  with  in  animals.  The  cones  are  most 
numerous  at  the  back  of  the  retina ;  they  are  fewer  in  number,  and  the 
rods  are  proportionally  more  numerous,  towards  the  anterior  part. 

The  pigmentary  layer  forms  the  most  external  part  of  the  retina.  It 
consists  of  hexagonal  epithelium-cells  (fig.  303),  which  are  smooth  exter- 
nally where  they  rest  against  the  choroid,  but  are  prolonged  internally 
into  fine  filaments  which  extend  between  the  rods.  The  pigment-granules, 
many  of  which  are  in  the  form  of  minute  crystals,  lie  in  the  inner 


FIG.  305.— VERTICAL  SECTION  THROUGH  THE  MACULA  LUTEA  AND  FOVEA  CENTRALIS  ; 
DIAGRAMMATIC  (after  M.  Sclmltze). 

1,  nerve-layer;  2,  ganglionic  layer;  3,  inner  molecular;  4,  inner  nuclear ;  and  5,  outer 
molecular  layers ;  6,  outer  nuclear  layer,  the  inner  part  with  only  cone-fibres  forming 
the  so-called  external  fibrous  layer ;  7,  cones  and  rods. 

part  of  the  cell,  and  after  prolonged  exposure  to  the  light  they  are 
found  extending  along  the  cell-processes  between  the  rods  (Kiihne), 
their  function  being  probably  connected  with  the  restoration  of  the 
purple  colouring  matter  which  has  been  bleached  by  the  light.  This 
extension  of  the  pigment  is  accompanied  by  a  shortening  of  the  cones 
(Engelmann). 

Fibres  of  MuUer.—The  fibres  of  Miiller  (fig.  297,  fig.  301,  J,  and 
fig.  304)  are  long  stiff  fibres  which  pass  through  several  of  the  retinal 
layers.  Commencing  at  the  inner  surface  of  the  retina  by  expanded 
bases  which  unite  with  one  another  to  form  the  so-called  internal 
limiting  membrane  (fig.  297),  the  fibres  pass  through  all  the  layers  in 
succession,  until  they  reach  the  outer  nuclear  layer.  Here  they  branch 
and  expand  into  a  sort  of  reticular  tissue  which  serves  to  support  the 


STEUCTUEE  OF  THE  EETINA.  273 

fibres  and  nuclei  of  the  rod-and-cone  elements.  At  the  bases  of  the 
rods  and  cones,  this  sustentacular  tissue  ceases,  being  here  bounded  by 
a  distinct  margin  which  has  been  called  the  external  limiting  membrane 
(fig,  304,  m.e.L),  but  delicate  sheaths  pass  from  it  round  the  bases  of 
the  rods  and  cones.  Each  Miillerian  fibre,  as  it  passes,  through  the 
inner  nuclear  layer,  has  a  nucleated  enlargement  (n),  indicating  the 
original  cell-nature  of  the  fibre. 

There  are  two  parts  of  the  retina  which  call  for  special  description. 

The  macula  lutea  (yellow  spot,  fig.  305),  with  its  central  fovea,  lies 
in  the  visual  axis,  and  is  the  part  of  the  retina  which  is  most  immedi- 
ately concerned  in  direct  vision.  It  is  characterised  firstly  by  its 


FlG.  306. — A  SMALL  PORTION  OF  THE 
CILIARY     PART     OF      THE      RETINA. 

(Kolliker.)    (350  diameters. ) 

1,  pigment-cells  ;  2,  columnar  cells.  % 


greater  thickness  (except  at  the  middle  of  the  fovea),  secondly  by  the 
large  number  of  ganglion-cells,  which  are  all  distinctly  bipolar  (2),  and 
thirdly  by  the  large  number  of  cones  it  contains  as  compared  with  the 
rods.  In  the  central  fovea  itself  there  are  no  rods,  and  the  cones  are 
very  long  and  slender ;  all  the  other  layers  become  gradually  thinned 
down  almost  to  complete  disappearance,  so  that  the  middle  of  the 
central  fovea  is  the  thinnest  part  of  the  retina.  Since  there  are  few 
rods,  the  outer  nuclear  layer  (6)  loses  in  great  measure  its  appear- 
ance of  being  composed  of  closely  packed  nuclei,  and  the  cone-fibres  are 
very  distinct.  The  direction  of  all  the  fibres  is  very  oblique  in  this 
part  of  the  retina. 

The  pars  ciliaris  retinae,  which  commences  at  the  ora  serrata,  where 
the  retina  proper  abruptly  ends,  is  composed  of  two  epithelial  layers 
(fig.  306),  and  has  no  nervous  structures.  Of  the  two  layers,  the 
external  is  a  thick  stratum  of  pigmented  epithelium  formed  of  rounded 
cells  and  continuous  with  the  pigmentary  layer  of  the  retina  on  the 
one  hand,  and  with  the  uvea  of  the  iris  on  the  other ;  the  inner  is  a 
layer  of  columnar  cells,  each  containing  an  oval  nucleus. 

The  retina  contains  but  few  blood-vessels.  The  artery  enters  and 
the  vein  leaves  it  in  the  middle  of  the  optic  nerve.  The  larger  vessels 
ramify  in  the  nerve-fibre  layer,  and  there  are  capillary  networks  in 
this  layer  and  in  the  inner  nuclear  layer.  There  are  perivascular 
lymphatic  spaces  around  the  veins  and  capillaries.  The  neural  epithe- 
lium receives  no  blood-vessels,  but  is  nourished  from  the  vessels  of  the 

choroid. 

s 


274 


THE  ESSENTIALS  OF  HISTOLOGY. 


FIG.  307.— SECTION  THROUGH  THE  MARGIN  OF  THE  RABBIT'S  LENS,  SHOWING  THE 

TRANSITION  OP  THE  EPITHELIUM   INTO  THE  LENS-FIBRES.      (Babuchin.) 


FIG.  308. — FIBRES  OF  THE  CRYSTALLINE  LENS.     (350  diameters.) 

A,  longitudinal  view  of  the  fibres  of  the  lens  from  the  ox,  showing  the  serrated  edges.  B, 
transverse  section  of  the  fibres  of  the  lens  from  the  human  eye.  C,  longitudinal  view 
of  a  few  of  the  fibres  from  the  equatorial  region  of  the  human  lens.  Most  of  the  fibres 
in  C  are  seen  edgeways,  and,  towards  1,  present  the  swellings  and  nuclei  of  the  '  nuclear 
zone ' ;  at  2,  the  flattened  sides  of  two  fibres  are  seen.  (A  and  B  from  Kolliker ;  C 
from  Henle.) 


STRUCTURE  OF  THE  LENS  AND  VITREOUS  HUMOUR,     275 

Structure  of  the  lens. — The  lens  is  a  laminated  fibrous  body  in- 
closed by  a  transparent  elastic  capsule  to  which,  around  the  circum- 
ference, the  fibres  of  the  suspensory  ligament  are  attached.  Immedi- 
ately within  the  capsule,  in  front  and  at  the  sides,  there  is  a  layer  of 
cubical  epithelium  termed  the  epithelium  of  the  capsule,  but  at  the 
margin  of  the  lens  the  cells  become  longer  and  pass  by  a  gradual 
transition  into  the  lens-fibres  (fig.  307).  The  fibres  which  compose  the 
lens  are  long  and  riband-shaped,  with  finely  serrated  edges  (fig.  308,  A) ; 
in  transverse  section  they  appear  prismatic  (B).  Many  of  the  superficial 
fibres  are  nucleated  (c),  the  lens-fibres  having  originally  been  developed 
by  the  elongation  of  epithelium-cells. 

The  vitreous  humour  is  composed  of  soft  gelatinous  tissue,  appa- 
rently structureless  when  examined  in  the  fresh  condition,  but  contain- 
ing a  few  scattered  amoeboid  cells,  the  processes  of  which  are  often  long 
and  varicose,  and  the  cell-bodies  distended  by  large  vacuoles.  The 
hyaloid  membrane,  which  invests  the  vitreous  humour,  is  homogeneous 
and  structureless  except  in  the  region  of  the  ciliary  processes,  where  it 
is  fibrous  in  structure,  forming  the  zonule  of  Zinn  and  spreading  out 
into  the  suspensory  ligament  of  the  lens.  This  part  of  the  hyaloid 
membrane  is  connected  with  a  circular  fibrous  portion  of  the  vitreous 
humour  which  serves  to  give  additional  firmness  to  the  attachment  of 
•the  fibres  of  the  suspensory  ligament  of  the  lens  (A.  Stuart). 


276  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  XLIV. 

STRUCTURE  OF  THE  OLFACTORY  MUCOUS  MEMBRANE 
AND  OF  THE  EXTERNAL  AND  MIDDLE  EAR. 

1 .  VERTICAL  sections  of  the  olfactory  mucous  membrane.  The  sections  may 
be  carried  either  across  the  middle  turbinate  bone,  after  decalcification  in 
0P2  per  cent,  chromic  acid,  or  across  the  upper  part  of  the  nasal  septum. 
Make  a  sketch  under  the  low  power.  Notice  the  difference  in  the  character 
of  the  epithelium  in  the  olfactory  and  respiratory  parts  of  the  membrane. 

2.  Teased  preparation  of  the  epithelium  of  the  olfactory  mucous  mem- 
brane.    A  piece  of  the  membrane  is  placed  quite  fresh  in  osmic  acid  ( 1  per 
cent.)  for  a  few  hoars,  and  is  then  macerated  for  two  days  or  more  in  water. 
The  epithelium  is  broken  up  in  dilute  glycerine  ;  the  cells  easily  separate 
from  one  another  on  tapping  the  cover-glass.     Notice  the  two  kinds  of  cells. 
Sketch  some  of  the  cells  under  a  high  power.1 

3.  Sections  of  the  external  ear  (these  have  been  already  studied  for  the 
cartilage,  Lesson  XII.). 

4.  Sections  across  the  cartilaginous  part  of  the  Eustachian  tube.     Sketch 
under  the  low  power. 

5.  Preparation  of  the  membrana  tympani.      A  piece  of  the  membrane, 
stained  with  haematoxylin,  and  mounted  flat  in  Canada  balsam. 

Determine  the  composition  of  the  membrane — i.e.  the  several  layers  com- 
posing it — by  focussing  carefully  with  the  high  power. 


STRUCTURE  OF  THE  OLFACTORY  MUCOUS  MEMBRANE. 

The  olfactory  region  of  the  nasal  fossae  includes  the  upper  and  middle 
turbinate  processes  and  the  upper  third  of  the  septum.  It  is  covered 
by  a  soft  vascular  mucous  membrane  of  a  yellow  colour  in  man. 

The  epithelium  of  the  olfactory  mucous  membrane  (figs.  309,  310)  is 
very  thick  and  is  composed  of  long  tapering  cells,  set  closely  side  by 
side  and  bounded  superficially  by  a  cuticular  lamina,  through  which  the 
free  ends  of  the  cells  project.  The  cells  are  of  two  kinds  :  1.  Long 
narrow  spindle-shaped  or  bipolar  cells  consisting  of  a  larger  part  or 
body  (I),  containing  the  nucleus,  and  of  two  processes  or  poles,  one  (c) 
straight  and  cylindrical  and  extending  to  the  free  surface,  the  other  (</) 

1  For  investigating  the  connection  of  the  olfactory  cells  with  the  olfactory  nerve-fibres, 
the  method  of  Golgi  must  be  employed. 


THE  OLFACTORY  MEMBRANE. 


277 


very  delicate  and  varicose,  looking  not  unlike  a  nerve-fibril  and  extending 
down  towards  the  cerium.  The  position  of  the  nuclear  enlargement 
varies,  and  with  it  the  relative  length  of  the  two  processes.  The  distal 
or  free  process  terminates  in  a  small  clear  projection,  which  passes 
beyond  the  cuticular  membrane  ;  in  amphibia,  reptiles,  and  birds,  and 


FIG.  309. — CELLS  AND  TERMINAL  NERVE- FIBRES  OF  THE  OLFACTORY  REGION. 

(M.  Schultze.)     (Highly  magnified.) 

1,  from  the  frog  ;  2,  from  man  ;  a,  epithelial  cell,  extending  deeply  into  a  ramified  process  ; 
b,  olfactory  cells ;  c,  their  peripheral  rods  ;  e,  their  extremities,  seen  in  1  to  be  prolonged 
into  fine  hairs  ;  d,  their  central  filaments. 

perhaps  in  some  mammals,  it  bears  fine  stiff  hairlike  filaments  (e).  The 
proximal  or  varicose  process  becomes  lost  amongst  the  plexus  of  olfac- 
tory nerve-fibrils  at  the  base  of  the  epithelium ;  it  is  connected  with 
one  of  the  fibrils  and  ultimately  passes  through  the  cribriform  plate  of 
the  ethmoid  to  end  in  an  arborisation  within  one  of  the  olfactory 
glomeruli  (see  diagram,  fig.  285,  p.  252).  These  cells  have  been  termed 
olfactory  cells.  2.  Long  columnar  epithelium-cells  (a},  with  compara- 
tively broad  cylindrical  nucleated  cell-bodies  placed  next  the  free 
surface,  and  long,  forked,  and  branching  tail-like  processes  extending 
down  to  the  corium.  These  are  usually  regarded  not  as  sensory  epithe- 
lium-cells, but  merely  as  serving  to  support  the  proper  olfactory  cells. 
They  are  the  columnar  or  sustentacular  cells.  3.  Tapering  cells  are  pre- 
sent, at  least  in  some  animals,  in  the  deeper  part  of  the  epithelium. 
They  rest  by  their  bases  upon  the  corium,  and  project  between  the 
•other  cells,  which  they  assist  to  support. 


278  THE  ESSENTIALS  OF  HISTOLOGY. 

The  corium  of  the  olfactory  mucous  membrane  is  also  very  thick 
(fig.  310).  It  contains  numerous  blood-vessels,  bundles  of  the  olfactory 
nerve-fibres  (which  are  non-medullated),  and  a  large  number  of  serous 
glands  known  as  Bowman's  glands  (b),  wrhich  open  upon  the  surface  by 
fine  ducts  passing  between  the  epithelium-cells. 


FIG.  310.— SECTION  OF  OLFACTORY  MUCOUS  MEMBRANE.    (Cadiat.) 
a,  epithelium  ;  6,  glands  of  Bowman  ;  c,  nerve-bundles. 

STRUCTURE  OF  THE  AUDITORY  ORGAN. 

The  external  ear  proper  (pinna)  is  composed  of  elastic  fibro -cartilage, 
invested  by  a  thin,  closely  adherent  skin.  The  skin  is  covered  by 
small  hairs,  and  connected  with  these  are  the  usual  sebaceous  follicles. 
In  some  parts — e.g.  the  lobule — there  is  a  considerable  amount  of 
adipose  tissue ;  and  voluntary  muscular  fibres  are  in  places  attached  to 
the  cartilage,  and  may  therefore  be  seen  in  sections  of  the  ear. 

The  external  auditory  meatus  is  a  canal  formed  partly  of  cartilage 
continuous  with  that  of  the  pinna,  partly  of  bone.  It  is  lined  by  a 
prolongation  of  the  skin  and  is  closed  by  the  membrana  tympani,  over 
which  the  skin  is  prolonged  as  a  very  thin  layer.  Near  the  orifice  the 
skin  has  hairs  and  sebaceous  glands,  and  the  meatus  is  also  provided 
throughout  the  cartilaginous  part  with  small  convoluted  tubular  glands 
of  a  brownish-yellow  colour,  which  yield  a  waxy  secretion  (ceruminous 
glands).  They  appear  to  represent  modified  sweat-glands. 

The  tympanum  is  lined  by  a  mucous  membrane  which  is  continuous 
through  the  Eustachian  tube  with  the  mucous  membrane  of  the 
pharynx ;  it  is  also  prolonged  into  the  mastoid  cells.  The  epithelium 


STRUCTURE  OF  THE  EUSTACHIAN  TUBE.  279 

is  columnar  and  ciliated  in  some  parts,  but  in  others — e.g.  roof,  promon- 
tory, ossicles,  and  membrana  tympani — it  is  a  pavement-epithelium. 

The  membrana  tympani  is  a  thin  membrane  formed  of  fibrous 
bundles  which  radiate  from  the  umbo.  Within  the  radial  fibres  are  a 
few  annular  bundles.  Covering  the  fibrous  membrane  externally  is  a 
thin  layer  continuous  with  the  skin  of  the  meatus;  covering  it  internally 
is  another  thin  layer,  derived  from  the  mucous  membrane  of  the 
tympanic  cavity.  Blood-vessels  and  lymphatics  are  distributed  to  the 
membrane  chiefly  in  the  cutaneous  and  mucous  layers. 

The  Eustachian  tube  is  the  canal  leading  from  the  tympanum  to  the 
pharynx.  It  is  formed  of  bone  near  the  tympanum,  but  below,  near 


FlG.  311. --SECTION  ACROSS  THE  CARTILAGINOUS  PAET  OF  THE  EUSTACHIAN  TUBE. 

(Riidinger.) 

1,  2,  bent  cartilaginous  plate  ;  3,  muse,  dilatator  tubse ;  to  the  left  of  4,  part  of  the  attach- 
ment of  the  levator  palati  muscle  ;  5,  tissue  uniting  the  tube  to  the  base  of  the  skull ; 
6  and  7,  mucous  glands ;  8,  10,  fat ;  9  to  11,  lumen  of  the  tube ;  12,  connective  tissue  on 
the  lateral  aspect  of  the  tube. 

the  pharynx,  it  is  bounded  partly  by  a  bent  piece  of  cartilage  (fig.  311, 
1,  2),  partly  by  fibrous  tissue.  The  latter  contains  numerous  mucous 
glands  (6,  7),  which  open  into  the  tube,  and  on  the  outer  side  a  band  of 
muscular  tissue  (3)  which  joins  the  tensor  palati.  The  epithelium  is 
ciliated. 


280  THE  ESSENTIALS  OF  HISTOLOGY. 


LESSON  XLV. 

STRUCTURE  OF  THE  LABYRINTH. 

1.  SECTIONS   across  one  of  the  membranous  semicircular   canals   of   a   fish 
(skate). 

2.  Longitudinal   sections   through   the   ampulla   of    a   semicircular   canal 
(skate). 

1  and  2  may  be  hardened  in  chromic  and  osmic  acid  (see  below  under  3) 
and  embedded  in  celloidin. 

3.  Vertical   sections   through   the   middle  of   the   cochlea   of   a   mammal 
(guinea-pig). 

The  cochlea  is  put  quite  fresh  into  O2  per  cent,  chromic  acid  containing  a 
few  drops  of  1  per  cent,  osmic  acid,  or  into  Flemming's  solution  (see  Appendix). 
When  decalcified,  it  is  well  washed,  and  then  placed  in  spirit  for  a  day  or 
more. 

In  preparing  sections  of  the  above  three  preparations  it  is  advisable,  in 
order  that  the  epithelium  should  be  kept  in  position,  to  embed  in  celloidin 
or,  if  the  paraffin  method  of  embedding  be  preferred,  to  fix  them  to  the  slide 
by  an  adhesive  process.  They  should  previously  be  stained  in  bulk. 

4.  Teased  preparations  of  the  auditory  epithelium  of  an  ampulla  or  of  the 
macula  of  the  utricle,  from  the  fish. 

5.  Teased  preparations  of  the  epithelium  of  the  organ  of  Corti  from  the 
guinea-pig. 

Both  4  and  5  are  made  from  osmic  preparations. 

Make  sketches  from  all  these  preparations  under  the  high  power.1 


The  labyrinth,  which  is  the  essential  part  of  the  auditory  organ, 
consists  of  a  complex  membranous  tube  lined  by  epithelium  and  filled 
with  endolymph,  contained  within  a  bony  tube — the  osseous  labyrinth 
— of  corresponding  complexity  of  shape  (figs.  312,  313).  The  mem- 
branous labyrinth  does  not  wholly  fill  the  bony  cavity ;  the  rest  of  the 
space  is  occupied  by  perilymph.  The  membranous  labyrinth  (fig.  312) 
is  composed  of  the  utricle  (u),  and  the  three  semicircular  canals,  each 
with  an  enlargement  or  ampulla  which  opens  into  it,  the  saccule  (s) 
and  the  canal  of  the  cochlea  (c.c.). 

The  ^tranches  of  the  auditory  nerve  pass  to  certain  parts  only  of  the 
membranous  labyrinth,  viz. — the  maculae  of  the  utricle  and  saccule  ; 

*For  the  methods  of  obtaining  the  various  parts  of  the  labyrinth  for  microscopical 
examination,  the  reader  is  referred  to  the  author's  Course  of  Practical  Histology. 


STRUCTURE  OF  THE  LABYRINTH. 


281 


the  cristse  of  the  ampullae,  and  along  the  whole  length  of  the  canal  of 
the  cochlea  (the  shaded  parts  in  fig.  312). 

At  these  places  the  lining  epithelium  is  specially  modified  to  form 
a,  sensory  or  nerve-epithelium;  elsewhere  it  is  a  simple  pavement- 
epithelium. 


s.s.c. 


s.e. 


FIG.  312.— PLAN  OF  THE  RIGHT  MEM- 
BRANOUS LABYRINTH  VIEWED  FROM 
THE  MESIAL  ASPECT.  2£ 

r 

u,  utricle,  with  its  macula  and  the  three 
semicircular  canals  with  their  ampullae ; 
s,  saccule ;  aq.v.,  aquseductus  vestibuli; 
s.e.,  saccus  endolymphaticus ;  c.r.,  canalis 
reunions  ;  c.c.  canal  of  the  cochlea. 


FIG.  313.— VIEW  OF  THE  INTERIOR  OF 
THE  LEFT  OSSEOUS  LABYRINTH. 

The  bony  wall  of  the  labyrinth  is  removed 
superiorly  and  externally.  1,  fovea  hemi- 
elliptica ;  2,  fovea  hemisphajrica  ;  3,  com- 
mon opening  of  the  superior  and  posterior 
semicircular  canals ;  4,  opening  of  the 
aqueduct  of  the  vestibule  ;  5,  the  superior, 
6,  the  posterior,  and  7,  the  external  semi- 
circular canals  ;  8,  spiral  tube  of  the  coch- 
lea ;  9,  scala  tympani ;  10,  scala  vestibuli. 


The -membranous  semicircular  canals  and  the  utricle  and  saccule 
are  composed  of  fibrous  tissue,  which  is  adherent  along  one  side  to  the 
endosteum  of  the  bony  canal ;  from  the  opposite  side  bands  of  fibrous 
tissue  pass  across  the  perilymph.  Within  the  fibrous  membrane  is  a 
thick  clear  tunica  propria,  which,  in  the  semicircular  canals,  forms 
papillary  elevations  in  the  interior  of  the  tube  (figs.  314,  315). 

The  places  of  entrance  of  the  nerve-fibres  into  the  ampullae  are 
marked  by  a  transverse,  inwardly  projecting  ridge  (crista),  in  the 
saccule  and  utricle  by  a  thickening  of  the  tunica  propria  (macula). 
The  epithelium  at  these  places  is  formed  of  columnar  cells  (fig.  316), 
which  are  surmounted  by  long,  stiff,  tapering  hairs  (auditory  hairs, 
fig.  316,  h),  and  to  these  hair-cells  the  axis-cylinders  of  the  nerve-fibres 
pass  directly  (fig.  317);  they  are  therefore — like  the  rod-and-cone- 
elements  of  the  retina,  the  bipolar  cells  of  the  olfactory  membrane,  and 
the  gustatory  cells  of  the  taste-buds — sensory  or  nerve-epithelium  cells. 
Between  them  are  a  number  of  thin  and  somewhat  rigid  nucleated 
cells  (fibre-cells  of  Retzius,  fig.  317,  /),  which  rest  upon  the  basement- 
membrane,  and  are  connected  at  their  free  extremity  with  a  cuticular 
membrane,  through  which  the  auditory  hairs  project. 


282 


THE  ESSENTIALS  OF  HISTOLOGY. 


FIG.  314.— SECTION  OF  ONE  OF  THE  HUMAN  SEMICIRCULAR  CANALS.    (Rudin<>-er.) 

(Magnified.) 

1,  osseous  wall ;  2,  fibrous  bands  with  included  blood-vessels,  united  at  3  with  the  peri- 
osteum ;  4,  membranous  canal  with  its  three  layers;  5,  short  fibrous  bands  (with 
intervening  spaces)  uniting  the  membranous  canal  firmly  to  the  periosteum  ;  6,  union 
of  its  outermost  layer  with  the  periosteum. 


FIG.  315.— SECTION  OF  MEMBRANOUS  SEMICIRCULAR  CANAL.     (Riidinger.) 
(Much  magnified.) 

1,  outer  fibrous  layer ;  2,  tunica  propria ;  3,  6,  papilliform  projections  with  epithelial 
covering ;  5,  fixed  side  of  the  canal,  with  very  thin  tunica  propria  without  papillse ; 
V,  fibrous  bands  passing  to  periosteum. 


STRUCTUKE  OF  THE  LABYRINTH. 


FIG.  316. — LONGITUDINAL  SECTION  OF  AN  AMPULLA  THEOUGH  THE  CRISTA  ACUSTICA. 

amp.,  cavity  of  the  ampulla  ;  sc.c.,  semicircular  canal  opening  oxit  of  it ;  c,  connective  tissue 
attached  to  the  wall  of  the  membranous  ampulla  and  traversing  the  perilymph  ;  e,  e, 
flattened  epithelium  of  ampulla  ;  h,  auditory  hairs  projecting  from  the  columnar  cells 
of  the  auditory  epithelium  into  the  cupula,  cup.  term. ;  v,  blood-vessels  ;  n,  nerve-fibres 
entering  the  base  of  the  crista  and  passing  into  the  columnar  cells. 


FIG.  317. — AUDITORY  EPITHELIUM  FROM  THE  MACULA  ACUSTICA  OF  THE  SACCULE 
OF  AN  ALLIGATOR.     (Retzius.)     (Highly  magnified.) 

c,  c,  columnar  hair-cells ;  /,  /,  fibre-cells ;  n,  nerve-fibre,  losing  its  medullary  sheath  and 
passing  to  terminate  in  the  columnar  auditory  cells ;  A,  auditory  hair ;  h',  base  of 
auditory  hairs,  split  up  into  fibrils. 


284 


THE  ESSENTIALS  OF  HISTOLOGY. 


The  auditory  hairs  do  not  project  free  into  the  endolymph,  but  into 
a  soft  mucus-like  substance,  of  a  dome-like  form  in  the  ampullae  (fig. 
316),  and  which  in  the  saccule  and  utricle  has  a  mass  of  calcareous 
particles  (otoliths)  embedded  in  it. 


FIG.  318. —VERTICAL  SECTION  OF  THE  COCHLEA  OP  A  CALF.    (Kolliker.) 


n      sp.l 


FIG.  319. — VERTICAL  SECTION  OF  THE  FIRST  TURN  OF  THE  HUMAN  COCHLEA. 
(G.  Retzius.) 

s.v.,  scala  vestibuli;  s.t.,  scala  tympani ;  D.C.,  canal  of  the  cochlea;  sp.l.,  spiral  lamina; 
n,  nerve-fibres ;  l.sp.,  spiral  ligament;  str.v.,  stria  vascularis ;  s.sp.,  spiral  groove;  R, 
section  of  Reissner's  membrane  ;  I,  limbus  laminae  spiralis  ;  M.t.,  membrana  tectoria; 
t.C.,  tunnel  of  Corti ;  b.m.,  basilar  membrane  ;  k.i.,  h.e.,  internal  and  external  hair-cells. 

The  cochlea  consists  of  a  bony  tube  coiled  spirally  around  an  axis, 
which  is  known  as  the  columella  (fig.  318).  The  tube  is  divided 
longitudinally  by  a  partition  which  is  formed  partly  by  a  projecting 


STEUCTUKE  OF  THE  COCHLEA.  285 

lamina  of  bone  (spiral  lamina),  partly  by  a  flat  membrane  (basilar 
membrane),  into  two  parts  or  scalce ;  the  upper  (supposing  the  cochlea 
resting  base  downwards)  being  termed  the  scala  vestibuli  (fig.  319,  s.v.), 
the  lower  the  scala  tympani  (s.t.) ;  the  latter  is  closed  at  its  larger  end 
by  the  membrane  of  the  fenestra  rotunda.  The  scalse  are  lined  by 
endosteum,  and  are  filled  with  perilymph,  continuous  with  that  of  the 
rest  of 'the  osseous  labyrinth  at  the  commencement  of  the  scala  vestibuli ; 
they  communicate  at  the  apex  by  a  small  opening,  the  helicotrema. 

The  scala  vestibuli  does  not  occupy  the  whole  of  that  part  of  the 
bony  tube  of  the  cochlea  which  is  above  the  partition.  Its  outer  third 
is  cut  off  by  a  delicate  connective-tissue  membrane  (membrane  of  Reissner, 
fig.  319,  E),  which  springs  from  near  the  end  of  the  spiral  lamina,  arid 
passes  upwards  and  outwards  to  the  outer  wall,  thus  separating  a  canal 
(D  C)  triangular  in  section,  which  is  lined  by  epithelium,  and  represents 
the  membranous  labyrinth  of  the  cochlea  (canal  of  the  cochlea). 

Canal  of  the  cochlea.  —The  floor  of  the  canal  of  the  cochlea  is  formed 
(1)  of  the  extremity  of  the  spiral  lamina,  which  is  thickened  above  by  a 
peculiar  kind  of  connective  tissue,  forming  an  overhanging  projection 
known  as  the  limbus  (fig.  319,  /) ;  (2)  of  the  basilar  membrane  (b.m.), 
which  stretches  across  from  the  end  of  the  bony  lamina  to  the  outer 
wall,  and  is  attached  to  this  by  a  projection  of  reticular  connective 
tissue  termed  the  spiral  ligament  (l.sp.). 

The  basilar  membrane  is  composed  of  stiff,  straight  fibres,  which 
extend  from  within  out,  and  are  embedded  in  a  homogeneous  stratum. 
It  is  covered  below  by  a  layer  of  connective  tissue  continuous  with  the 
endosteum  of  the  scala  tympani ;  above,  the  modified  epithelium,  which 
forms  the  organ  of  Corti,  rests  upon  it.  It  becomes  gradually  broader  in 
the  upper  turns  of  the  cochlea  (rather  more  than  twice  as  broad  in  the 
uppermost  as  in  the  lowermost  turn),  and  its  constituent  fibres  become 
therefore  gradually  longer. 

The  organ  of  Corti  consists  of  the  following  structures  : 

1.  The  rods  of  Corti,  two  series  (inner  and  outer)  of  stiff",  striated 
fibres  of  a  peculiar  shape,  the  inner  rods  somewhat  like  a  human  ulna, 
the  outer  like  a  swan's  head  and  neck  (fig.  320).  They  rest  by  one  ex- 
tremity (the  foot)  on  the  basilar  membrane  a  short  distance  apart,  and 
are  inclined  towards  one  another,  their  larger  ends  (heads)  being  jointed 
together ;  the  series  of  rods  thus  inclose  a  sort  of  tunnel,  the  floor  of 
which  is  formed  by  a  part  of  the  basilar  membrane.  Close  to  their 
feet  may  usually  be  seen  the  remains  of  the  cells  from  which  they  have 
been  formed.  The  inner  rods  are  narrower  and  rather  more  numerous 
than  the  outer.  Each  outer  rod  has  a  process  which  extends  outwards 
and  is  known  as  the  phalangeal  process.  This  forms  part  of — 


286 


THE  ESSENTIALS  OF  HISTOLOGY. 


2.  A  reticular  lamina  (fig.  322,  /.r.),  which  is  a  cuticular  structure 
extending  like  a  wire-net  over  the  outer  epithelium-cells  of  the  organ 
of  Corti,  and  is  composed  of  two  or  three  series  of  stiff  fiddle-shaped 
rings  (phalanges)  cemented  together  in  such  a  manner  as  to  leave 
square  or  oblong  apertures  through  which  the  hair-cells  (see  below) 
project. 


FlG.  320.— A  PAIR  OF  EODS  OP  CORTI,    FROM  THE   RABBIT'S  COCHLEA,    IN  SIDE 

VIEW.     (Highly  magnified. ) 

b,  b,  basilar  membrane ;  i.r.,  inner  rod ;  e.r.,  outer  rod.    The  nucleated  protoplasmic  masses 
at  the  feet  are  also  shown. 

3.  The  outer  hair-cells  placed  external  to  the  rods  of  Corti.  These 
are  epithelium-cells  of  columnar  shape,  arranged  in  three  or  four  series 
(fig.  321,  p,  q,  r).  The  free  extremity  of  the  cell  is  surmounted  by  a 


FIG.  321.—  SECTION  OF  THE  ORGAN  OF  CORTI  OF  THE  DOG.    (Waldeyer.)    ^. 


a,  a',  end  of  spiral  lamina  ;  b,  c,  middle  (homogeneous)  layer  of  the  basilar  membrane  ;  u, 
vestibular  (striated)  layer  ;  v,  tympanal  (connective-tissue)  layer  ;  d,  blood-vessel  ;  /, 
nerves  in  spiral  lamina  ;  g,  epithelium  of  spiral  groove  ;  h,  nerve-fibres  passing  towards 
inner  hair-cells,  i,  k  ;  I,  auditory  hairlets  on  inner  hair-cells  ;  I,  i',  lamina  reticularis  ; 
m,  heads  of  the  rods  of  Corti,  jointed  together  ;  u,  base  of  inner  rods  ;  o,  base  of  outer 
rod  ;  p,  q,  r,  outer  hair-cells  ;  t,  lower  ends  of  hair-cells  ;  w,  nerve-fibrils  passing  across 
the  tunnel  of  Corti  ;  z,  cells  of  Deiters. 

bundle  of  short  auditory  hairs,  and  projects  through  one  of  the  apertures 
in  the  reticular  lamina  ;  the  fixed  extremity  is  prolonged  into  a  stift 
cuticular  process  (fig.  323,  pf),  which  is  attached  to  the  basilar  membrane. 
Between  them  are  other  supporting  cells  which  are  tapered  in  the  same 


STRUCTURE  OF  THE  COCHLEA. 


287 


FIG.  322.  —  SEMI-DIAGRAM- 
MATIC VIEW  OF  PART  OF 
THE  BASILAR  MEMBRANE 
AND  TUNNEL  OF  CORTI  OF 
THE  RABBIT,  FROM  ABOVE 
AND  THE  SIDE.  (Much 

magnified. ) 

/,  limbus ;  Cr.,  extremity  or 
crest  of  limbus  with  tooth-like 
projections;  b.b.,  basilar  mem- 
brane; sp.  I. , spiral  lamina  with, 
p,  perforations  for  transmission 
of  nerve-fibres  ;  i.r.,  fifteen  of 
the  inner  rods  of  Corti;  h.i., 
their  flattened  heads  seen  from 
above  ;  e.r. ,  nine  outer  rods  of 
Corti;  h.e.,  their  heads,  with 
the  phalangeal  processes  ex- 
tending outward  from  them 
and  forming,  with  the  two 
rows  of  phalanges,  the  lamina 
reticularis,  I.r.  At  the  lower 
part  of  the  figure  the  connect- 
ive-tissue fibres  and  nuclei  of 
the  undermost  layer  of  the 
basilar  membrane  are  seen 
through  the  upper  layers. 
Portions  of  the  basilar  pro- 
cesses of  the  outer  hair-cells 
remain  attached  here  and 
there  to  the  membrane  at  this 
part. 


r 


FIG.  323.— AN  OUTER  HAIR-CELL  IN  CONNECTION  WITH  ITS  BASILAR 
PROCESS.     From  the  guinea-pig.     (Highly  magnified.) 

Two  auditory  hairs  have  remained  attached  to  the  cell ;  b.  bulged  lower 
end  of  cell ;  p,  basilar  process,  protoplasmic  above,  but  becoming  cuti- 
cular  below,  and  slightly  expanded  at  the  extremity,  /,  which  is  broken 
•away  from  the  basilar  membrane. 


288  THE  ESSENTIALS  OF  HISTOLOGY. 

manner,  but  rest  by  their  larger  end  upon  the  basilar  membrane,  and 
are  prolonged  above  into  a  cuticular  process  which  is  attached  to  the 
reticular  lamina  (cells  of  Deiters,  fig.  321,  z). 

4.  The  inner  hair-cells  (fig.  321,  i),  placed  internal  to  the  rods  of 
Corti.  They  form  a  single  series  of  columnar  cells  surmounted  by 
auditory  hairs,  lying  in  close  apposition  to  the  inner  rods. 

The  rest  of  the  epithelium-cells  have  no  important  characteristics. 
They  are  long  and  columnar  next  to  the  outer  hair-cells,  but  soon 
diminish  in  size,  becoming  cubical,  and  in  this  form  they  are  continued 
over  the  outer  wall  of  the  cochlear  canal.  Here  they  cover  a  very  vas- 
cular membrane  (stria  vascularis,  fig.  319,  str.  v.),  which  is  frequently 
pigmented  :  its  capillary  blood-vessels  penetrate  between  the  epithelium- 
cells.  Internal  to  the  inner  hair-cells  the  epithelium  also  soon  becomes 
cubical ;  it  is  prolonged  in  this  form  over  the  limbus  of  the  spiral 
lamina.  The  epithelium  of  Reissner's  membrane  is  of  the  pavement 
variety. 

The  membrana  tectoria  (fig.  319,  M.t.)  is  a  soft,  fibrillated  structure, 
which  is  attached  along  the  upper  surface  of  the  limbus,  and  lies  like  a 
pad  over  the  organ  of  Corti.  It  thins  out  towards  the  distal  margin, 
here  becoming  somewhat  reticular,  and,  according  to  Retzius,  it  is 
attached  to  the  lamina  reticularis.  In  sections  it  usually  appears  raised 
a  short  distance  above  the  auditory  hairs,  but  it  is  probable  that  it 
always  rests  upon  them  during  life. 


FIG.  324. — GENERAL  VIEW  OF  THE  MODE  OF  DISTRIBUTION  OF  THE  COCHLEAE  NERVE, 

ALL  THE  OTHER  F;ARTS   HAVING  BEEN  REMOVED. 

The  fibres  of  the  cochlear  branch  of  the  auditory  nerve  enter  the  base 
of  the  columella,  and  run  in  canals  through  its  substance,  being  gradu- 
ally deflected  outwards  as  they  pass  upwards  into  the  spiral  lamina, 
at  the  base  of  which  they  swell  out  into  a  ganglionic  cord  (spiral 


STRUCTURE  OF  THE  COCHLEA.  289 

ganglion).     Many,  if  not  all  the  fibres,  are  connected  with  the  cells  of 
this  ganglion. 

After  traversing  the  spiral  lamina  they  emerge  in  bundles,  and  the 
fibres  then,  having  lost  their  medullary  sheath,  pass  into  the  epithe- 
lium of  the  inner  hair-cell  region.  Here  some  of  them  are  directly 
continuous  with  the  inner  hair-cells,  whilst  others  pass  in  the  form 
of  delicate  fibrils  across  the  tunnel  of  Corti,  to  become  applied 
to  the  outer  hair-cells  (fig.  321);  but  there  does  not  appear  to  be  a 
direct  continuity  in  this  case  between  the  nerve-fibrils  and  the  cell- 
substance. 


290  THE  ESSENTIALS  OF  HISTOLOGY. 


APPENDIX. 


General  Methods  of  Preserving  and  Hardening  Tissues  and  Organs.— 
The  fluids  which  are  most  commonly  used  are  alcohol,  chromic  acid  solution 
(1  in  200  to  1  in  500,  to  which  glacial  acetic  acid  may  advantageously  be 
added  in  the  proportion  of  2  parts  acetic  acid  to  1000  chromic  solution),  picric 
acid  solution  (saturated,  either  alone  or  containing  2  parts  of  sulphuric  acid 
to  1000),  osmic  acid  solution  (1  per  cent.),  bichromate  of  potash  solution  (2 
per  cent.),  Miiller's  fluid  (bichromate  of  potash  2J  parts,  sulphate  of  soda  1 
part,  water  100  parts),  Erlicki's  fluid  (which  is  the  same  as  Miiller's,  but  with 
sulphate  of  copper  in  place  of  sulphate  of  soda),  and  bichromate  of  ammonia 
(2  per  cent.).  For  preserving  the  structure  of  cells  and  nuclei  the  best 
general  fixing  and  hardening  fluid  is  that  recommended  by  Flemming.  This 
consists  of  15  vols.  of  1  per  cent,  chromic  acid,  4  vols.  of  2  per  cent,  osmic 
acid,  and  1  vol.  glacial  acetic  acid.  It  may  advantageously  be  diluted  with 
from  two  to  five  times  its  bulk  of  water  before  use.  The  following  methods 
of  hardening  the  several  tissues  and  organs  are  found  to  give  good  general 
results : — 

Tissue  or  Organ.  Hardening  Fluid. 

Bladder Chromic  acid  or  alcohol. 

Blood-vessels      ....     Alcohol  or  bichromate  of  potash. 
Brain          .....     Bichromate  of  ammonia  or  Miiller's 

fluid. 

Elastic  ligament         .         .         .     Bichromate  of  potash. 
Embryos    .....     Chromic  acid  or  picric  acid. 

Eye Miiller's  fluid. 

Eyelids       .....     Alcohol. 

Ganglia Picric  acid  or  Miiller's  fluid. 

Heart         .....     Alcohol  or  bichromate  of  potash. 
Injected  organs          .         .         .     Alcohol. 

Intestine    .....     Distend  with  chromic  acid  or  with 

a  mixture  of  equal  parts  alcohol 
and  I  per  cent,  chromic  acid  solu- 
tion, or  with  picric  acid. 

Kidney Miiller's  fluid. 

Lachrymal  gland        .         .         .     Alcohol. 

Larynx Chromic  acid. 

Liver  Miiller's  fluid. 


APPENDIX. 


291 


Lung 


Tissvie  or  Organ. 


Mammary  gland 
Marrow  of  bone 
Muscular  tissue,  striated  . 

,,  non-striated 

Nerve          .... 
(Esophagus 

Ovary          .... 
Pancreas    .... 
Retina        .... 
Salivary  glands . 
Sclerotic  and  cornea  . 
Skin  ..... 
Spinal  cord 

Spleen         .... 
Stomach 


Suprarenal  capsule     . 

Tendon  and  ligament 

Testis 

Thymus  gland   . 

Thyroid  gland    . 

Tongue 

Tonsils 

Trachea 

Ureter 

Uterus 


Hardening  Fluid. 

Distend  with  chromic  acid  or  with 
alcohol  and  chromic  acid. 

Alcohol. 

Alcohol. 

Alcohol. 

Chromic  acid. 

Picric  acid  or  osmic  acid. 

Distend  with  chromic  acid. 

Chromic  acid. 
Alcohol. 
Muller's  fluid. 

Alcohol. 

Alcohol  or  Muller's  fluid. 

Alcohol. 

Mtillers  fluid. 

Muller's  fluid,  picric  acid,  or  alcohol. 

Distend  with  chromic  acid,  or  with 
alcohol  and  chromic  acid,  or  with 
picric  acid. 
Alcohol. 
Alcohol. 
Alcohol. 
Alcohol. 
Alcohol. 

Muller's  fluid  or  alcohol. 
Alcohol. 

Chromic  acid  and  alcohol. 
Chromic  acid  and  alcohol. 
Chromic  acid  and  alcohol. 


Tissues  to  be  hardened  in  alcohol  should  usually  be  placed  at  once  in  strong 
methylated  spirit,  or,  better,  in  absolute  alcohol.  They  are  ready  for  cutting 
as  soon  as  they  are  dehydrated  ;  as  a  rule  they  may  be  left  indefinitely  in 
alcohol  without  deterioration.  Organs  which  contain  much  fibrous  tissue, 
such  as  the  skin  and  tendons,  should  not  go  into  strong  alcohol,  but  should 
be  hardened  in  about  70  per  cent,  strength  ;  otherwise  they  become  too  hard 
to  cut. 

For  tissues  that  are  to  be  hardened  in  chromic  acid  an  immersion  of  from 
7  to  14  days  is  generally  necessary ;  they  may  then  be  placed  in  alcohol  for 
preservation  and  to  complete  the  process  of  hardening.  The  spirit  should  be 
changed  once  or  twice. 

Organs  placed  in  bichromate  of  potash  or  Miiller's  fluid  are  ready  for 
section  in  a  fortnight  or  three  weeks  ;  they  may,  however,  be  left  for  a  much 
longer  time  in  those  fluids  without  deterioration.  With  picric  acid  the 
hardening  process  is  generally  complete  in  2  or  3  days  ;  the  organs  may 
then  be  transferred  to  spirit,  which  ought  to  be  frequently  changed. 


292  THE  ESSENTIALS  OF  HISTOLOGY. 

The  hardening  of  the  brain  and  spinal  cord  in  Mtiller's  fluid  takes  from 
3  weeks  to  as  many  months.  It  can  be  hastened  by  warmth  or  by  placing 
small  pieces  in  Marchi's  fluid  (see  below),  after  they  have  been  a  week  or  10 
days  in  Miiller. 

In  no  case  should  the  pieces  of  tissue  to  be  hardened  be  too  thick  for  the 
fluid  readily  to  penetrate  to  every  part.  They  should  be  taken  as  soon  after 
death  as  possible.  Each  piece  should  have  from  10  to  20  times  its  bulk  of 
hardening  fluid,  and  this  should  always  be  changed  after  a  few  hours. 

Embedding  of  Hardened  Tissues,  and  Preparation  of  Sections.- 
Sections  are  most  advantageously  made  with  some  form  of  microtome.  It  is 
generally  needful  to  support  the  hardened  tissue  whilst  it  is  being  cut,  and 
with  this  object  it  is  embedded  in  some  fatty  or  other  substance  which  is 
applied  to  it  in  the  fluid  condition  and  becomes  solid  on  standing.1  The  em- 
bedding substance  can  either  simply  inclose  the  tissue,  or  the  tissue  may  be 
soaked  in  it :  the  latter  method  is  the  one  most  commonly  employed. 

The  embedding  substance  chiefly  used  is  paraffin  of  110°  F.  (43°  C.)  melting 
point. 

Embedding  in  paraffin. — Before  being  soaked  in  melted  paraffin,  the  piece 
of  tissue  is  stained,  dehydrated  by  absolute  alcohol,  and  is  then  soaked  in 
turpentine,  xylol,  or  chloroform.  From  this  it  is  transferred  to  molten 
paraffin,  which  should  not  be  too  hot,  and  it  is  soaked  in  this  for  one  or 
several  hours,  according  to  thickness.  It  is  then  placed  in  the  desired  posi- 
tion on  the  microtome  and  surrounded  by  melted  paraffin.  When  cold,  thin 
sections  can  be  cut,  the  paraffin  dissolved  out  by  turpentine  or  xylol,  and  the 
sections  mounted. 

If  it  be  desired  to  cut  a  riband  of  successive  sections,  the  block  of  paraffin 
in  which  the  organ  is  embedded  must  be  cut  with  square  angles,  and  some 
paraffin  of  low  melting  point  smeared  over  the  opposite  sides  of  the  block. 

Preparation  of  frozen  sections. — The  bichromate  solutions  are  the  best 
fluids  to  use  for  preserving  tissues  which  are  to  be  frozen  in  place  of  being 
embedded.  The  tissue  requires  to  be  soaked  in  gum-water  before  being 
placed  upon  the  freezing  microtome. 

Embedding  in  celloidin. — The  piece  to  be  embedded  is  dehydrated  by 
alcohol,  and  is  then  placed  in  a  solution  of  celloidin  in  alcohol  and  ether. 
After  24  hours  or  more  it  is  removed  from  the  celloidin  and  placed  upon 
a  flat  wooden  or  metal  holder  (which  can  be  fixed  in  the  microtome  when 
the  celloidin  has  been  hardened).  When  the  celloidin  is  set,  the  holder 
is  plunged  in  alcohol  (80  per  cent.),  and  after  a  few  hours,  sections 
may  be  cut  with  a  knife  wetted  with  spirit  of  the  same  strength.  The 
advantage  of  this  method  is  that  the  celloidin,  which  is  quite  transparent, 
need  not  be  got  rid  of  in  mounting  the  sections,  and  serves  to  keep  the 
parts  of  a  section  together  :  it  is  thus  very  useful  for  friable  tissues  or  for 
large  sections.  The  tissue  may  either  be  stained  in  bulk  before  embedding, 
or  the  sections  may  be  stained.  The  method  is  especially  valuable  for  the 
central  nervous  system. 

1  For  rapid  work  a  split  piece  of  alcohol-hardened  liver  is  often  used  to  support  the 
tissue  from  which  sections  are  to  be  taken. 


APPENDIX. 


293 


Microtomes. — A  section-cutting  apparatus  or  microtome  is  essential  for 
liistological  work.  Several  kinds  are  made,  but  those  which  I  have  found 
most  generally  useful  are  the  freezing  microtome,  the  rocking  micro- 
tome of  the  Cambridge  Scientific  Instrument  Company  for  objects  which 
have  been  embedded  in  paraffin,  and  the  sliding  microtome  for  celloidin- 
embedded  tissues.  The  action  of  the  rocker  is  automatic ;  that  is  to 
say,  every  to-and-fro  movement  of  the  handle,  H,  not  only  cuts  a  section  of 
the  tissue  of  definite  thickness,  but  also  moves  the  paraffin  block  forwards 
in  readiness  for  the  next  section.  And  by  employing  a  rectangular  block 
of  paraffin  of  the  proper  consistency,  a  long  series  of  sections  of  the  same 
object,  of  equal  thickness,  can  be  obtained  and  made  to  adhere  together  in 


ROCKING  MICROTOME. 

a  riband  (as  shown  in  the  figure).  The  sections  can,  if  desired,  be  kept  in 
series  by  the  employment  of  the  creasote-shellac,  or  some  other  adhesive 
method  of  mounting  the  riband. 

In  the  freezing  microtome  the  tissue,  after  being  soaked  in  gum-water, 
is  placed  on  a  metal  plate  and  frozen  by  playing  an  ether  spray  on  the  under 
surface  of  the  plate.  The  plate  is  moved  upwards  by  a  finely  cut  screw, 
and  the  knife  or  plane  used  to  cut  the  sections  is  guided  over  the  plate  by 
passing  over  glass  slides.  In  using  the  freezing  microtome,  especially  for 
the  nervous  system,  it  is  important  not  to  freeze  the  tissue  too  hard,  or  the 
section  will  roll  up  like  an  ice-wafer. 

For  celloidin-embedded  preparations  it  is  necessary  to  cut  the  sections 
with  a  knife  kept  wetted  with  spirit.  For  this  purpose  a  sliding  microtome, 
in  which  the  knife  or  razor  is  moved  horizontally  over  the  tissue,  with  the 
edge  obliquely  inclined  to  the  direction  of  movement,  is  most  useful.  That 
designed  by  Thoma,  and  made  by  Jung  of  Heidleberg,  is  admirably  con- 


294  THE  ESSENTIALS  OF  HISTOLOGY. 

structed,  and  works  with  great  accuracy.  In  all  cases  it  is  most  important 
that  the  knife  should  be  in  perfect  order. 

Staining  and  Mounting  of  Sections.— The  fluids  most  commonly  em- 
ployed for  the  staining  of  sections  are  : — 1.  A  solution  of  hsematoxyliri  and 
alum  ;  2.  a  solution  of  carmine  ;  3.  a  solution  of  picro-carminate  of  ammonia. 
The  time  of  immersion  in  the  staining  fluid  varies  according  to  the  strength 
of  the  fluid  and  the  mode  by  which  the  tissue  has  been  hardened.  The  neces- 
sity of  staining  sections  may  be  avoided  if  the  piece  of  tissue  is  stained  in 
bulk  before  embedding.  For  this  purpose  either  Delati  eld's  or  Ehrlich's 
lumnatoxylin  may  be  used.  If  Delafield's  be  employed  the  piece  of  tissue  is 
left  to  stain  for  24  hours  or  more,  and  is  then  placed  for  15  to  30 
minutes,  according  to  thickness,  in  alcohol  containing  1  part  of  nitric  acid  per 
cent.  The  excess  of  stain  is  thereby  removed  and  the  sections  are  rendered  very 
clear  and  distinct  in  all  their  details.  If  Ehrlich's  is  used,  the  pieces  of  tissue 
should  be  thoroughly  washed  in  tap-water  for  an  hour  or  more  and  then 
transferred  to  alcohol.  For  some  purposes  an  alcoholic  solution  of  magenta 
is  used  for  staining  in  bulk  ;  from  this  the  tissue  goes  into  a  small  quantity 
of  oil  of  cloves,  and  after  being  soaked  with  this  it  is  passed  through  turpentine 
into  the  melted  paraffin. 

If  the  tissues  have  not  been  stained  in  bulk,  the  following  is  the  order  of 
transference  of  the  sections  (they  are  supposed,  if  cut  from  paraffin,  to  have 
been  freed  from  this  by  immersion  in  turpentine  or  xylol)  : — 

1.  From  turpentine  to  absolute  alcohol  (5  minutes). 

'2.  From  alcohol  to  distilled  water  (^  minute). 

3.  From  distilled  water  to  hsematoxylin,  which  for  staining  purposes  should 
be  diluted  with  distilled  water  and  filtered  (5  minutes  or  more). 

4.  From  hsematoxyliu  to  distilled  water  (^  minute). 

5.  From  distilled  water  to  alcohol  (2  or  3  minutes). 

6.  From  alcohol  to  oil  of  cloves1  (1  minute). 

7.  From  oil  of  cloves  to  Canada  balsam  solution. 

If  the  tissues  have  already  been  stained  in  bulk,  the  sections  are  simply 
mounted  in  Canada  balsam  after  the  paraffin  used  for  embedding  has  been 
dissolved  away  from  them  in  turpentine  or  xylol. 

Adhesive  methods  of  mounting. — Friable  sections,  such  as  sections  of  small 
embryos,  and  ribands  of  sections  such  as  are  cut  with  many  microtomes,  may 
be  mounted  in  the  following  way  : — The  slide  is  smeared  with  a  solution  of 
shellac  in  clove-oil,  the  sections  are  placed  in  this  and  warmed  so  as  to  melt 
their  paraffin.  They  are  thus  fixed  by  the  shellac,  and  the  slide  can  be  im- 
mersed in  turpentine  to  remove  the  paraffin,  and  the  sections  then  covered  in 
Canada  balsam.  For  this  method  the  tissue  should  have  been  previously 
stained  in  bulk. 

A  simpler  method,  but  one  which  answers  the  purpose  very  well,  is  to  place 
the  riband  or  pieces  of  paraffin  containing  the  sections  on  the  surface  of  warm 
water  (not  hot  enough  to  melt  the  paraffin),  to  float  the  sections  on  to  a  slide, 

1  Other  essential  oils,  such  as  oil  of  cedar,  oil  of  bergamot  and  xylol,  may  be  used 
instead  of  oil  of  cloves. 


APPENDIX.  295 

then  to  drain  off  the  water,  and  put  the  slide  and  sections  in  a  warm  chamber, 
hot  enough  to  melt  the  paraffin,  until  all  the  water  has  been  driven  off.  The 
sections  are  then  found  to  have  adhered  firmly  to  the  slide,  and  the  paraffin 
can  be  removed  by  washing  the  slide  with  xylol  or  immersing  it  in  xylol.  If 
not  previously  stained  they  can  then  be  passed  through  alcohol  into  stain  and" 
afterwards  again  through  alcohol  and  xylol,  previous  to  mounting  in  Canada 
balsam. 

For  single  sections  it  is  often  sufficient  to  place  them  in  a  drop  of  water,  or 
water  and  spirit,  on  the  slide,  drain  off  the  water  and  then  keep  the  paraffin 
melted  until  the  water  has  been  entirely  driven  off. 

The  following  are  some  of  the  principal  staining  solutions  and  methods  of 
staining  for  special  purposes  : — 

1.  Delafield  hcemato.vylin. — To  150  cubic  centimeters  of  a  saturated  solu- 
tion of  alum  in  water,  add  4  cubic  centimeters  of  a  saturated  solution  of 
hsematoxylin  in  alcohol.     Let  the  mixture  stand  8  days,  then  decant,  and 
add  25  cubic  centimeters  of  glycerine,  and  25  cubic  centimeters  of  methylic 
alcohol. 

For  staining  sections  add  a  few  drops  of  this  solution  to  a  watchglassful 
of  distilled  water.  If  overstained  the  excess  of  colour  can  be  removed  by 
alcohol  containing  1  per  cent,  nitric  acid.  With  long  keeping  this  solution 
becomes  red  instead  of  blue  ;  a  trace  of  ammonia  will  restore  the  requisite 
colour. 

2.  Ehrlich  hcematoxylin. — Dissolve  2  grammes  hsematoxyliii  in  100  cubic 
centimeters  alcohol ;  add  100  cubic  centimeters  water,  100  cubic  centimeters 
of  glycerine,  and  10  cubic  centimeters  glacial  acetic  acid.     This  solution  will 
keep  almost  indefinitely  :  it  is  valuable  for  staining  in  bulk,  as  it  does  not 
overstain  tissues.     For  staining  sections  it  is   best  to  dilute  the  solution 
either  with  distilled  water  or  with  30  per  cent,  alcohol.     After  the  sections 
have  been  stained  they  must  be  thoroughly  washed  with  tap  water.     This 
develops  the  blue  colour  of  the  hsematoxylin. 

3.  Kultschitzky  hcematoxylin. — Dissolve  1  gramme  hsematoxylin  in  a  little 
alcohol,  and  add  to  it  100  cubic  centimeters  of  a  2  per  cent,  solution  of  acetic 
acid.     This  solution  is  valuable  for  staining  sections  of  the  nervous  system 
(modified  Weigert-Pal  process). 

4.  Kleinenberg    hcematoxylin.  —  This    serves   well   for   staining   in    bulk. 
Saturate  70  per  cent,  alcohol  first  with  calcium  chloride  and  then  with  alum, 
and  after  filtration  add  six  to  eight  volumes  of  70  per  cent,  alcohol. 

Take  a  freshly  prepared  saturated  solution  of  haematoxylin  in  absolute 
alcohol,  and  add  it  drop  by  drop  to  the  above  mixture  until  it  is  of  a  distinct 
purplish  colour. 

This  solution  improves  on  keeping.  It  may  if  necessary  be  diluted  with 
more  of  the  mixture. 

5.  ffeidenhairis  method. — After  hardening  in  alcohol,  or  in  saturated  solu- 
tion of  picric  acid  and  then  alcohol,  place  the  tissue  for  12  to  24  hours  in 
a  ^  per  cent,  watery  solution  of  hsematoxylin,  and  then  from  12  to  24  hours 
more  in  a  ^  per  cent,  solution  of  yellow  chromate  of  potash.     Now  place  in 
alcohol,  pass  through  xylol,  and  embed  in  paraffin. 


296  THE  ESSENTIALS  OF  HISTOLOGY. 

6.  Carminate  of  ammonia. — Prepared  by  dissolving  carmine  in  ammonia 
and  allowing  the  excess  of  ammonia  to  escape  by  slow  evaporation.     The 
salt  should  be  allowed  to  dry  and  be  dissolved  in  water  as  required. 

7.  Picro-carminate  of  ammonia  (picro-carmine,  Eanvier). — To  a  saturated 
solution  of  picric  acid  add  a  strong  ammoiiiacal  solution  of  carmine,  until  a 
precipitate  begins  to  form.     Evaporate  on  the  water-bath  (or,  better,  allow 
it  to  evaporate  spontaneously)  to  ith  ;  filter  from  the  sediment  and  evaporate 
the  filtrate  to  dryness.     Make  a  5  per  cent,  solution  of  the  residue,  diluting 
further  as  required. 

8.  Lithium-carmine. — Dissolve  2J  grammes  of  carmine  in  100  cubic  centi- 
meters  of   a   saturated   solution   of    lithium   carbonate.      This   solution    is 
valuable  for  staining  pieces  of  tissue  in  bulk.     They  may  be  left  in  it  for 
24  hours  or  more,  and   should  then  be   placed  in  acidulated  alcohol  (see 
below).     Sections  may  be  stained  by  it  in  a  few  minutes.     The  addition  of 
2  to  3  times  its  volume  of   saturated   solution  of  picric  acid  to  the  above 
solution  of  carmine  in  lithium  carbonate  has  been  recommended  as  a  ready 
and  convenient  way  of  preparing  picro-carmine. 

9.  Borax-carmine. — Dissolve  4  grammes  borax  and  3  grammes  carmine  in 
100  cubic  centimeters  of  warm  water.     Add  100  cubic  centimeters  of  70  per 
cent,  alcohol,  filter  and  let  stand.     This  solution  improves  on  keeping.      It  is 
useful  for  staining  in  bulk. 

After  staining  with  lithium-carmine  or  borax-carmine,  the  tissue  should  in 
all  cases  be  placed  in  70  per  cent,  alcohol  containing  5  drops  of  hydrochloric 
acid  to  100  cubic  centimeters. 

10.  Magenta. — Take  5  cubic  centimeters  of  a  1  per  cent,  alcoholic  solution 
of  magenta,  and  to  it  add  gradually  20  cubic  centimeters  glycerine.     Dilute 
with  water  to  100  cubic  centimeters.     This  solution  is  for  fresh  tissues  and 
for  sections  to  be  mounted  in  glycerine.     For  sections  to  be  mounted  in 
Canada  balsam  a  solution  in  alcohol  is  used. 

11.  Safranin. — A  saturated  alcoholic  solution  is  used   for   staining  cell- 
nuclei.     The  tissue- elements  having  been  fixed  by  dilute  chromic  and  acetic 
acid,  or  by  Flemming's  solution,  small  shreds  or  thin  sections  are  placed  for 
12  to  24  hours  in  a  little  of  the  solution,  mixed  with  half  its  bulk  of  water. 
The  shreds  are  rinsed  in  absolute  alcohol  (which  may  contain  a  little  free 
hydrochloric  acid)  until  the  colour  is  washed  out  from  everything  except  the 
nuclei ;    they  are  then  at   once  transferred  to  clove-oil,  and  from  this  are 
mounted  in  Canada  balsam. 

12.  Aniline  blue-black. — Dissolve  1  gramme  of  aniline  blue-black  in  a  mix- 
ture of  30  parts  of  water  with  20  of  alcohol.     This  is  sometimes  used  for 
staining  sections  of  the  central  nervous  system. 

13.  Marches  solution. — This  is  a  mixture  of  Miiller's  fluid  (2  parts)  with  1 
per  cent,  osmic  acid  (1  part).     It  is  of  great  value  for  staining  nerve-fibres  in 
the  earlier  stages  of  degeneration,  before  sclerosis  sets  in  (especially  a  few 
days  after  the  establishment  of  a  lesion).     All  the  degenerated  medullated 
fibres  are  stained  black,  whilst  the  rest  of  the  section  remains  almost  un- 
stained.    It  is  best  to  put  thin  pieces  of  the  brain  or  cord  to  be  investigated 
into  a  large  quantity  of  the  solution  (after  previously  hardening  for  10  days 


APPENDIX.  297 

in  Miiller's  fluid),  and  to  leave  them  in  it  for  a  week  or  more  ;  but  if  necessary 
sections  can  be  stained  ;  in  this  case  they  are  left  in  the  solution  for  a  few  hours. 
In  either  case  they  are  mounted  by  the  usual  process  in  Canada  balsam. 

14.  Weigert-Pal  method. — This  method  is  of  great  value  for  the  central 
nervous  system.     By  it  all  medullated  nerve-fibres  are  stained  dark,  while 
the  grey  matter  and  any  degenerated  tracts  of  white  matter  are  left  un- 
coloured.     The  following  modification  of  the  original  method  can  be  very 
strongly  recommended  : — Pieces  which  have  been  hardened  in  Miiller's  fluid 
and  afterwards  kept  a  short  time  in  alcohol  (without  washing  in  water)  are 
embedded  in  celloidin,  and  sections  are  cut  as  thin  as  possible.     Or  sections 
may  be  made  of  the  tissue  direct  from  Miiller's  fluid,  if  it  is  first  soaked  in 
gum-water  for  a  few  hours.     In  either  case  they  are  placed  in  water,  and 
from  this  are  transferred  to  Marchi's  fluid  (see  above,  sec.  13),  in  which  they 
are  left  for  a  few  hours.     They  are  then  again  washed  in  water  and  trans- 
ferred to  acetic  acid  hsematoxylin  (see  above,  sec.  3).     In  this  they  are  left 
overnight,  by  which  time  they  will  be  completely  black.     After  again  wash- 
ing in  water  they  are  ready  to  be  bleached.      This  is  accomplished  by  Pal's 
method  as  follows  :— Place  the  overstained  sections,  first  in  j  per  cent,  solu- 
tion of  potassic  permanganate  for  5  minutes  ;  rinse  with  water  and  transfer 
to  Pal's  solution  (sulphite  of  soda  1  gramme,  oxalic  acid  1  gramme,  distilled 
water,  200  cubic  centimeters),  in  which  the  actual  bleaching  takes  place. 
They  are  usually  sufficiently  differentiated  in  a  few  minutes  :  if  not,  they  can 
be  left  longer  in  the  solution  without  detriment.     If  after  half  an  hour  they 
are  not  differentiated  enough,  they  must  be  put  again  (after  washing)  into 
the  permanganate  for  some  minutes,  and  then   again   into  Pal's  solution. 
After  differentiation  they  are  passed  through  water,  alcohol,  and  oil  of  ber- 
gamot  (or  xylol),  to  be  mounted  in  Canada  balsam.     The  advantages  which 
this  modification   has   over   the   original   methods   are   (1)   the   very  finest 
medullated  fibres  are  brought  to  view  with  great  surety  ;  (2)  the  staining 
of  the  fibres  is  jet  black,  and  offers  a  strong  contrast  to  the  colourless  grey 
matter  ;   (3)  the  sections  are  easily  seen  and  lifted  out  of  the  acid  hsema- 
toxylin,    which  has  very  little  colour  ;  (4)  it  is  difficult  to  overbleach  the 
sections  ;  (5)  the  stain  is  remarkably  permanent. 

15.  Stainmg  with  chloride  of  gold. — a.  Cohnheim's  method. — Place  the  fresh 
tissue  for  from  30  to  60  minutes  in  a  J  per  cent,  solution  of  chloride  of 
gold  ;  then  wash  and  transfer  to  a  large  quantity  of  water  just  acidulated 
with  acetic  acid.     Keep  for  2  or  3  days  in  the  light  in  a  warm  place.     This 
answers  very  well  for  the  cornea.     If  it  be  principally  desired  to  stain  the 
nerve-fibrils  within  the  epithelium,  the  cornea  may  be  transferred  after  24 
hours  to  a  mixture  of  glycerine  (1  part)  and  water  (2  parts),  and  left  in  this 
for  24  hours  more. 

/3.  Lowifs  method. — Place  small  pieces  of  the  fresh  tissue  in  a  mixture  of 
1  part  of  formic  acid  to  2  to  4  parts  of  water  for  £  to  1  minute  ;  then  in  1  per 
cent,  chloride  of  gold  solution  for  10  to  15  minutes  ;  then  back  again  into  the 
formic  acid  mixture  for  24  hours  and  into  pure  formic  acid  for  24  hours  more. 
After  removal  from  the  gold,  and  whilst  in  the  acid,  the  tissue  must  be  kept 
in  the  dark. 


298  '  THE  ESSENTIALS  OF  HISTOLOGY. 

y.  Ranvier's  method. — Immerse  in  lemon-juice  for  5  to  10  minutes,  then 
wash  with  water  and  place  in  1  per  cent,  gold  chloride  solution  for  20 
minutes.  Then  treat  either  as  in  Cohnheim's  or  as  in  Lowit's  method. 

16.  Staining  with  nitrate  of  silver. — Wash  the  fresh  tissue  with  distilled 
water  ;  immerse  in  £  to  1  per  cent,   nitrate  of  silver  solution  for  5  to  10 
minutes  ;  rinse  with  distilled  water  and  expose  to  bright  sunlight  either  in 
water,  alcohol,  or  glycerine.     This  method  is  used  to  exhibit  endothelium  and 
generally  to  stain  intercellular  substance. 

17.  Golffi's   nitrate   of  silver  methods. — These   are   chiefly   employed  for 
investigating  the  relations  of  cells  and  fibres  in  the  central  nervous  system- 
Two  methods  are  mostly  used,  as  follows  : — 

a.  Very  small  pieces  of  the  tissue  which  has  been  hardened  for  some  weeks 
in  bichromate  solution  or  Miiller's  fluid  are  placed  for  half  an  hour  in  the 
dark  in  0*75  per  cent,  nitrate  of  silver  solution,  and  are  then  transferred  for 
24  hours  or  more  to  a  fresh  quantity  of  the  same  solution  (to  which  a  drop 
or  two  of  formic  acid  may  be  added).  They  may  then  be  hardened  with  50 
per  cent,  alcohol,  and  sections,  which  need  not  be  thin,  are  cut  either  from 
celloidin  with  a  microtome  or  with  the  free  hand.  The  sections  are  mounted 
in  Canada  balsam,  which  is  allowed  to  dry  011  the  slide  :  they  must  not  be 
covered  with  a  cover-glass,  but  the  balsam  must  remain  exposed  to  the  air. 

ft.  Instead  of  being  slowly  hardened  in  bichromate,  the  tissue  is  placed  at 
once  in  very  small  pieces  in  a  mixture  of  bichromate  and  osmic  (3  parts  of 
Miiller's  fluid  to  1  of  osmic  acid).  In  this  it  remains  from  2  to  5  days,  after 
which  the  pieces  are  treated  with  silver  nitrate  as  in  the  other  case.  This 
method  is  not  only  more  rapid  than  the  other,  but  is  more  sure  in  its  results. 

18.  'EhrlicKs  methyl-blue  method. — This  method  is  one  of  great  value  for 
exhibiting  nerve-terminations,  and  in  some  cases  the  relations  of  nerve-cells 
and  fibres  in  the  central  nervous  system.     For  its  application  the  tissue  must 
be  living  :  it  is  therefore  best  applied  by  injecting  a  solution  of  methyl-blue 
(4  parts  to  100  of  saline  solution)  into  the  blood-vascular  or  into  the  lymphatic 
system,  but  good  results  can  also  sometimes  be  obtained  by  immersing  small 
pieces  of  freshly -excised  living  tissue  in  a  less  concentrated  solution  (0*2  per 
cent.).     In  either  case  the  tissue  must  be  spread  out  in  a  thin  layer  freely 
exposed  to  the  air  ;  the  blue  colour  then  appears  in  the  nerve-cells  and  axis- 
cylinders,  even  to  their  finest  ramifications.     To  fix  the  stain  the  tissue  is 
treated  for  some  hours  with  saturated  solution  of  picrate  of  ammonia,  after 
which  the  preparation  can  be  mounted  in  glycerine. 

Mounting  Solutions  : — 1.  Saline  solution. — A  0'6  per  cent,  solution  of 
common  salt  is  used  in  place  of  serum  for  mounting  fresh  tissues  for  imme- 
diate examination. 

2.  Glycerine,  either  pure  or  diluted  with  water.     The  cover-glass  may  be 
fixed  by  gold  size. 

3.  Canada  balsam,  from  which  the  volatile  oils  have  been  driven  off  by 
heat,  dissolved  in  xylol. 


INDEX. 


INDEX. 


ADE 

ADENOID  tissue,  44. 
Adipose  tissue,  41. 
Angioblasts,  117. 
Aorta,  structure  of,  110. 
Appendix,  290. 
Areolar  tissue,  38. 
Arrector  pili,  137. 
Arteries,  nerves  of,  111. 

—  variation  in  structure  of,  110. 

—  and  veins,  smaller,  structure  of,  112. 
Artery,  coats  of,  107. 

Attraction  particle,  2. 
Auerbach,  plexus  of,  174. 


BASEMENT  membranes,  44. 
Bile-ducts,  185. 
Bladder,  201. 
Blastoderm,  4. 

Blood-corpuscles,  action  of  reagents 
upon,  15. 

—  coloured,  12. 

—  colourless,  12,  16. 

—  amoeboid  phenomena  of,  22. 

—  migration    from     blood-vessels, 
115. 

—  development  of,  13. 

—  enumeration  of,  10. 

—  of  amphibia,  18. 
Blood-crystals,  16. 
Blood-tablets,  13. 

Blood-vessels,  development  of,  117. 
Bone,  57. 

—  development  of,  64. 

—  lacunas  and  canaliculi  of,  58. 

—  lamellae  of,  58. 

—  marrow  of,  62. 

Bowman,  ciliary  muscle  of,  265. 

—  membrane  of,  261. 

—  glands  of,  278. 
Bronchi,  144. 
Bronchial  tubes,  146. 

Brain.  See  Cerebrum,  Cerebellum, 
Medulla  oblongata,  Mesencephalon, 
Pons  Varolii. 

—  membranes  of,  256. 


DES 

CAPILLARIES,  113. 

—  circulation  in,  114. 
Cartilage,  articular,  51. 

—  costal,  54. 

—  embryonic,  53. 

—  hyaline,  51. 

—  transitional,  51. 

—  varieties  of,  50. 
Cartilage -cells,  51. 

—  capsules  of,  52. 
Celloidin  for  embedding,  292. 
Cells,  division  of,  4,  25. 

—  embryonic,  4. 

—  structure  of,  1. 

Central  tendon  of  diaphragm,  112. 
Cerebellum,  241. 
Cerebrum,  244. 

—  basal  ganglia  of,  253. 
Choroid  coat  of  eye,  262. 
Chromic  acid,  241. 
Chromoplasm,  3. 
Chromosomes,  26. 
Ciliary  movement,  35. 

—  muscle,  265. 
Clarke,  column  of,  221. 
Cochlea,  284. 
Cohnheim,  areas  of,  73. 
Colostrum-corpuscles,  215. 
Conjunctiva,  258. 
Connective  tissue,  cells  of,  40. 
development  of,  48. 

—  jelly-like,  44. 

—  tissues,  38. 
Cornea,  261. 

Corpora  quadrigemina,  238. 
Corpus  luteum,  212. 

—  striatum,  253. 
Corti,  organ  of,  285. 
Cotton  fibres,  9. 
Crusta  petrosa,  152. 
Cutis  vera,  129. 

DEITEBS,  process  of,  93. 
Dentine,  150. 

—  formation  of,  153. 
Descemet,  membrane  of,  262. 


300 


THE  ESSENTIALS  OF  HISTOLOGY. 


DOB 

Dobie,  line  of,  74. 
Doyere,  eminence  of,  105. 
Dust,  9. 

EAR,  278. 

Ebner,  glands  of,  156. 

Ehrlich's  methyl-blue  method,  298. 

Elastic  tissue,  46. 

Eleidin,  129. 

Embedding,  methods  of,  292. 

Enamel,  149. 

—  formation  of,  153. 
End-bulbs,  98. 
Endocardium,  141. 
Endomysium,  74. 
Endoneurium,  88. 
Enclothelium,  28. 
End-plates,  103. 
Epicardium,  141. 
Epidermis,  127. 
Epididymis,  203. 
Epineurium,  88. 
Epithelium,  24. 

—  ciliated,  32. 

—  classification  of,  27. 

—  columnar,  30. 

—  stratified,  27. 

— •  structure  and  division  of  cells,  24, 
25. 

—  transitional,  33. 
Erectile  tissue,  201. 
Erlicki's  fluid,  290. 
Eustachian  tube,  279. 
Eye,  257. 

Eyelids,  258. 
Eye-piece,  7. 

FALLOPIAN  tubes,  213. 
Fat,  absorption  of,  178. 
Fat-cells,  41. 

Fenestrated  membrane,  108. 
Fibres,  elastic,  39. 

—  white,  of  connective  tissue,  39. 
Fibrin,  13. 

Fibro-cartilage,  elastic,  55. 

—  white,  55. 
Fibrous  tissue,  46. 
Flemming's  solution,  290. 
Freezing   method   for  preparation   of 

sections,  293. 

GALL-BLADDER,  185. 
Ganglia,  91. 
Ganglion-cells,  93. 
Gas-chamber,  35. 
Gland,  thymus,  124. 

—  pineal,  254. 
Glands,  anal,  180. 

—  ceruminous,  137,  278. 

—  gastric,  169. 

—  lachrymal,  261. 


LIE 

Glands,  lymphatic,  121. 

—  mammary,  215. 

—  Meibomian,  259. 

—  of  Bowman,  278. 

—  of  Cowper,  202. 

—  of  Littre,  202. 

—  salivary,  161. 

—  sebaceous,  137. 

—  sudoriparous,  137. 
Glomeruli  of  kidney,  193. 
Glycogen     in     colourless      blood-cor- 
puscles, 19. 

Goblet-cells,  31. 
Gold-methods,  297. 
Golgi,  organ  of,  103. 

—  method   of  preparing  the  nervous 
system,  298. 

Graanan  follicles,  211. 
Grandry,  corpuscles  of,  101. 
Ground-substance  of  connective  tissue, 

39. 
Gullet.     See  (Esophagus. 

ILEMATOIDIN,  16. 

Heemin,  16. 

Haemoglobin,  16. 

Hair-cells  of  auditory  organ,  281,  286, 

288. 

Hair-follicle,  structure  of,  132. 
Hairs,  9,  132. 

—  development  of,  111. 

—  muscles  of,  137. 
Haversian  canals,  58. 

—  systems,  59. 
Heart,  139. 

Henle,  fenestrated  membrane  of,  108. 

—  looped  tubules  of,  193. 

—  sheath  of,  89. 
Hensen,  line  of,  73. 
Hepatic  lobules,  181. 
Hippocampus,  250. 
Histology,  meaning  of  term,  1. 
Hyaloplasm,  2. 

INTESTINE,  large,  179. 

—  small,  174. 
Iris,  266. 

JELLY  of  Wharton,  419. 

KAHYOKINESIS,  4,  25. 
Kidney,  192. 
—  blood-vessels  of,  197. 
Krause,  membrane  of,  74. 

LABYRINTH  of  ear,  280. 

Lacteals,  178. 

Lanugo,  136. 

Larynx,  144. 

Lens,  275. 

Lieberkiihn,  crypts  of,  177. 


INDEX. 


301 


LIN 

Linen  fibres,  9. 
Liver,  181. 
Lung,  146. 

—  alveoli  of,  146. 

—  blood-vessels  of,  148. 
Lymphatic  glands,  121. 
Lymphatics,  115. 

—  connection  with  cells  of  connective 
tissue,  41,  117. 

—  development  of,  117. 
Lymph-corpuscles,  12. 
Lymphoid  tissue,  44,  125. 

MACULA  lutea  of  retina,  273. 

Malpighian  corpuscles  of  kidney,  193. 

Malpighian  corpuscles  of  spleen,  187. 

Marchi's  fluid,  296. 

Marrow,  62. 

Medulla  oblongata,  227. 

Meissner,  plexus  of,  176. 

Mesencephalon,  237. 

Methods  of  embedding,  292. 

—  of  mounting  sections,  293. 

—  of  preparing  sections,  292. 

— •  of  preserving  and  hardening,  290. 

—  of  staining,  293. 
Micrometer,  7. 
Microscope,  choice  of,  6. 

—  structure  of,  6. 

Microscopic  work,  requisites  for,  6. 
Microtomes,  292. 

Migration  of  colourless  blood-cor- 
puscles, 22,  115. 
Moist  chamber,  34. 
Mould,  9. 

Mounting  solutions,  298. 
Mucous  membranes,  29. 
Muller,  fibres  of,  272. 
Mtiller's  fluid,  290. 
Muscle,  blood-vessels  of,  80. 

—  development  of,  80. 

—  ending  of,  in  tendon,  79. 

—  involuntary  or  plain,  82. 
• —  nerves  of,  85. 

—  of  insects,  75,  76. 

—  of  heart,  81. 

—  structure  of,  compared  with  proto- 
plasm, 78. 

—  voluntary,  72. 
Muscle-corpuscles,  74. 
Myeloplaxes,  62. 
Myocardium,  139. 

NAILS,  131. 

Nerve-cells,  91. 

Nerve-fibres,  axis-cylinder  of,  86. 

—  degeneration  of,  97. 

—  medullated,  83. 

medullary  segments  of,  85. 

—  sheath  of,  84. 
motor,  terminations  of,  103. 


SAK 

Nerve-fibres,-non -medullated,  87. 
—  sensory,  modes  of  termination 
of,  98,  101. 

—  trunk,  structure  of,  88. 
Nervi  nervorum,  89. 
Neuroglia,  97. 
Neurokeratin,  87. 
Nucleoli,  3. 

Nucleus,  3. 

OBJECTIVE,  7. 
Ocular,  7. 
(Esophagus,  166. 
Olfactory  bulb,  252. 
-  cells,  277. 

—  mucous  membrane,  276. 

—  tract,  251. 
Omentum,  112. 
Optic  thalamus,  254. 
Ossification  in  cartilage,  64. 

—  in  membrane,  70. 
Osteoblasts,  62,  65. 
Osteoclasts,  68. 
Osteogenic  fibres,  70. 
Ovary,  209. 

Ovum,  4,  211. 

PACINIAN  corpuscles,  101. 
Pancreas,  185. 
Papillae  of  tongue,  156. 

—  of  skin,  130. 
Paraplasm,  2. 
Penis,  201. 
Pericardium,  141. 
Perineurium,  88. 
Periosteum,  61. 
Peyer,  patches  of,  177. 
Pharynx,  165. 

Pia  mater,  216. 
Pituitary  body,  254. 
Pleura,  148. 
Pons  Varolii,  233. 
Portal  canal,  182. 
Prickle-cells,  28. 
Prostate,  202. 
Protoplasm,  2. 
Purkinje,  cells  of,  241. 

—  fibres  of,  142. 

BANVIEK,  nodes  of,  85. 
Kemak,  fibres  of,  87. 
Eetiform  tissue,  43. 
Eetina,  267. 

—  macula  lutea  of,  273. 

—  pars  ciliaris  of,  273. 

SACCULE,  281. 
Saline  solution,  298. 
Salivary  glands,  161. 

—  corpuscles,  24,  124. 
Sarcolemma,  72. 


302 


THE  ESSENTIALS  OF  HISTOLOGY. 


SAB 

Sarcomeres,  76. 
Sarcoplasm,  73. 
Sarcostyles,  73. 
Sarcous  elements,  76. 
Schwann,  sheath  of,  83. 
Sclerotic  coat  of  eye,  261. 
Sections,  preparation  of,  292. 
Semicircular  canals,  281. 
Seminiferous  tubules,  203. 
Serous  membranes,  118. 
Sharpey,  fibres  of,  59. 
Silver-methods,  297. 
Skin,  127. 

Spermatogenesis,  207. 
Spermatozoa,  206. 
Spinal  cord,  216. 

—  blood-vessels  of,  226. 

—  central  canal  of,  224. 

characters  in  different  parts,  224. 

—  membranes  of,  216. 

—  nerve  cells  of,  221. 

tracts  in,  219. 

Spleen,  187. 
Spongioplasm,  2. 
Staining  of  sections,  293. 
Starch  granules,  7. 
Stomach,  167. 

—  glands  of,  169. 

—  blood-vessels  of,  171. 

—  lymphatics  of,  172. 
Stomata,  118. 
Suprarenal  capsule,  189. 
Synovial  membranes,  120. 

TACTILE  corpuscles,  98. 
Taste-buds,  156. 
Tendon,  48. 

—  cells,  47. 


YEA 

Tendon,  nerve  endings  in,  103. 
Testicle,  202. 
Thymus  gland,  124. 
Thyroid  body,  191. 
Tissues,  enumeration  of,  1. 

—  formation   from   blastodermic 
layers,  4. 

Tongue,  156. 
Tonsils,  123. 
Tooth,  149. 

—  formation  of,  152. 

—  pulp  of,  152. 
Trachea,  143. 
Tympanum,  278. 

URETER,  200. 

Urethra,  202. 

Urinary  bladder,  201. 

Uriniferous  tubules,  course  of,  193. 

Uterus,  213. 

Utricle,  281. 

VAS  deferens,  205. 
Vasa  vasorum,  111. 
Vaso-formative  cells,  117. 
Veins,  structure  of,  110. 

—  variations  in,  111. 
Vesiculas  seminales,  206. 
Villi,  177. 

Vitreous  humour,  275. 

WARMING  apparatus,  20. 
Weigert-Pal  method  for  staining  sec- 
tions of  the  nervous  system,  296. 
Woollen  fibres,  9. 

YEAST,  8. 


GLASGOW  :    PRINTED  AT  THE   UNIVERSITY   PRESS  BY   ROBERT   MACLKHOSE. 


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